2
Indexing

This chapter describes the various elements you can use to create your Oracle Text index.

The following topics are discussed in this chapter:

• Overview
• Datastore Types
• Filter Types
• Lexer Types
• Wordlist Type
• Storage Types
• Section Group Types
• Classifier Types
• Stoplists
• System-Defined Preferences
• System Parameters

Overview

When you use CREATE INDEX to create an index or ALTER INDEX to manage an index, you can optionally specify indexing preferences, stoplists, and section groups in the parameter string. Specifying a preference, stoplist, or section group answers one of the following questions about the way Oracle indexes text:

Preference Class	Answers the Question
Datastore	How are your documents stored?
Filter	How can the documents be converted to plain text?
Lexer	What language is being indexed?
Wordlist	How should stem and fuzzy queries be expanded?
Storage	How should the index tables be stored?
Stop List	What words or themes are not to be indexed?
Section Group	Is querying within sections enabled, and how are the document sections defined?

This chapter describes how to set each preference. You enable an option by creating a preference with one of the types described in this chapter.

For example, to specify that your documents are stored in external files, you can create a datastore preference called mydatastore using the FILE_DATASTORE type. You specify mydatastore as the datastore preference in the parameter clause of CREATE INDEX.

Creating Preferences

To create a datastore, lexer, filter, wordlist, or storage preference, you use the CTX_DDL.CREATE_PREFERENCE procedure and specify one of the types described in this chapter. For some types, you can also set attributes with the CTX_DDL.SET_ATTRIBUTE procedure.

To create a stoplists, use CTX_DDL.CREATE_STOPLIST. You can add stopwords to a stoplist with CTX_DDL.ADD_STOPWORD.

To create section groups, use CTX_DDL.CREATE_SECTION_GROUP and specify a section group type. You can add sections to section groups with CTX_DDL. ADD_ZONE_SECTION or CTX_DDL.ADD_FIELD_SECTION.

Datastore Types

Use the datastore types to specify how your text is stored. To create a datastore preference, you must use one of the following datastore types:

Datastore Type	Use When
DIRECT_DATASTORE	Data is stored internally in the text column. Each row is indexed as a single document.
MULTI_COLUMN_DATASTORE	Data is stored in a text table in more than one column. Columns are concatenated to create a virtual document, one per row.
DETAIL_DATASTORE	Data is stored internally in the text column. Document consists of one or more rows stored in a text column in a detail table, with header information stored in a master table.
FILE_DATASTORE	Data is stored externally in operating system files. Filenames are stored in the text column, one per row.
NESTED_DATASTORE	Data is stored in a nested table.
URL_DATASTORE	Data is stored externally in files located on an intranet or the Internet. Uniform Resource Locators (URLs) are stored in the text column.
USER_DATASTORE	Documents are synthesized at index time by a user-defined stored procedure.

DIRECT_DATASTORE

Use the DIRECT_DATASTORE type for text stored directly in the text column, one document per row. DIRECT_DATASTORE has no attributes.

The following columns types are supported: CHAR, VARCHAR, VARCHAR2, BLOB, CLOB, BFILE, or XMLType.

DIRECT_DATASTORE CLOB Example

The following example creates a table with a CLOB column to store text data. It then populates two rows with text data and indexes the table using the system-defined preference CTXSYS.DEFAULT_DATASTORE.

create table mytable(id number primary key, docs clob); 

insert into mytable values(111555,'this text will be indexed');
insert into mytable values(111556,'this is a direct_datastore example');
commit;

create index myindex on mytable(docs) 
  indextype is ctxsys.context 
  parameters ('DATASTORE CTXSYS.DEFAULT_DATASTORE');

MULTI_COLUMN_DATASTORE

Use this datastore when your text is stored in more than one column. During indexing, the system concatenates the text columns and indexes the text as a single document.

MULTI_COLUMN_DATASTORE has the following attributes:

Attribute

Attribute Value

columns

Specify a comma separated list of columns to be concatenated during indexing. You can also specify any expression allowable for the select statement column list for the base table. This includes expressions, PL/SQL functions, column aliases, and so on. NUMBER and DATE column types are supported. They are converted to text before indexing using the default format mask. The TO_CHAR function can be used in the column list for formatting. RAW and BLOB columns are directly concatenated as binary data. LONG, LONG RAW, NCHAR, and NCLOB, nested table columns and collections are not supported. The column list is limited to 500 bytes.

Indexing and DML

To index, you must create a dummy column to specify in the CREATE INDEX statement. This column's contents are not made part of the virtual document, unless its name is specified in the columns attribute.

The index is synchronized only when the dummy column is updated. You can create triggers to propagate changes if needed.

MULTI_COLUMN_DATASTORE Security

Only CTXSYS is allowed to create preferences for the MULTI_COLUMN_DATASTORE type. Any other user who attempts to create a MULTI_COLUMN_DATASTORE preference receives an error.

Oracle makes this restriction because when the columns attribute contains a function call, the call is made by the CTXSYS schema. The potential exists for a malicious CTXAPP users to execute arbitrary functions for which they do not have execute permission.

If this is too restrictive, you can create a stored procedure under CTXSYS to create MULTI_COLUMN_DATASTORE preferences. The effective user is CTXSYS, who creates and owns the preferences. However, you can call this procedure from any schema as CTXSYS.

MULTI_COLUMN_DATASTORE Example

The following example creates a multi-column datastore preference called my_multi with three text columns:

begin


ctx_ddl.create_preference('my_multi', 'MULTI_COLUMN_DATASTORE');
ctx_ddl.set_attribute('my_multi', 'columns', 'column1, column2, column3');

end;

Tagging Behavior

During indexing, the system creates a virtual document for each row. The virtual document is composed of the contents of the columns concatenated in the listing order with column name tags automatically added. For example:

create table mc(id number primary key, name varchar2(10), address varchar2(80));
insert into mc values(1, 'John Smith', '123 Main Street');

exec ctx_ddl.create_preference('mymds', 'MULTI_COLUMN_DATASTORE');
exec ctx_ddl.set_attibute('mymds', 'columns', 'name, address');

This produces the following virtual text for indexing:

<NAME>
John Smith
</NAME>
<ADDRESS>
123 Main Street
</ADDRESS>

The system indexes the text between the tags, ignoring the tags themselves.

Indexing Columns as Sections

To index these tags as sections, you can optionally create field sections with the BASIC_SECTION_GROUP.

When you use expressions or functions, the tag is composed of the first 30 characters of the expression unless a column alias is used.

For example, if your expression is as follows:

exec ctx_ddl.set_attibute('mymds', 'columns', '4 + 17');

then it produces the following virtual text:

<4 + 17>
21
</4 + 17>

If your expression is as follows:

exec ctx_ddl.set_attibute('mymds', 'columns', '4 + 17 col1');

then it produces the following virtual text:

<col1>
21
<col1>

The tags are in uppercase unless the column name or column alias is in lowercase and surrounded by double quotes. For example:

exec ctx_ddl.set_attibute('mymds', 'COLUMNS', 'foo');

produces the following virtual text:

<FOO>
content of foo
</FOO>

For lowercase tags, use the following:

exec ctx_ddl.set_attibute('mymds', 'COLUMNS', 'foo "foo"');

This expression produces:

<foo>
content of foo
</foo>

DETAIL_DATASTORE

Use the DETAIL_DATASTORE type for text stored directly in the database in detail tables, with the indexed text column located in the master table.

DETAIL_DATASTORE has the following attributes:

Attribute	Attribute Value
binary	Specify TRUE for Oracle to add no newline character after each detail row. Specify FALSE for Oracle to add a newline character (\n) after each detail row automatically.
detail_table	Specify the name of the detail table (OWNER.TABLE if necessary)
detail_key	Specify the name of the detail table foreign key column(s)
detail_lineno	Specify the name of the detail table sequence column.
detail_text	Specify the name of the detail table text column.

Synchronizing Master/Detail Indexes

Changes to the detail table do not trigger re-indexing when you synchronize the index. Only changes to the indexed column in the master table triggers a re-index when you synchronize the index.

You can create triggers on the detail table to propagate changes to the indexed column in the master table row.

Example Master/Detail Tables

This example illustrates how master and detail tables are related to each other.

Master Table Example

Master tables define the documents in a master/detail relationship. You assign an identifying number to each document. The following table is an example master table, called my_master:

Column Name	Column Type	Description
article_id	NUMBER	Document ID, unique for each document (Primary Key)
author	VARCHAR2(30)	Author of document
title	VARCHAR2(50)	Title of document
body	CHAR(1)	Dummy column to specify in CREATE INDEX

Detail Table Example

Detail tables contain the text for a document, whose content is usually stored across a number of rows. The following detail table my_detail is related to the master table my_master with the article_id column. This column identifies the master document to which each detail row (sub-document) belongs.

Column Name	Column Type	Description
article_id	NUMBER	Document ID that relates to master table
seq	NUMBER	Sequence of document in the master document defined by article_id
text	VARCHAR2	Document text

Detail Table Example Attributes

In this example, the DETAIL_DATASTORE attributes have the following values:

Attribute	Attribute Value
binary	TRUE
detail_table	my_detail
detail_key	article_id
detail_lineno	seq
detail_text	text

You use CTX_DDL.CREATE_PREFERENCE to create a preference with DETAIL_DATASTORE. You use CTX_DDL.SET_ATTRIBUTE to set the attributes for this preference as described earlier. The following example shows how this is done:

begin


ctx_ddl.create_preference('my_detail_pref', 'DETAIL_DATASTORE');
ctx_ddl.set_attribute('my_detail_pref', 'binary', 'true');
ctx_ddl.set_attribute('my_detail_pref', 'detail_table', 'my_detail');
ctx_ddl.set_attribute('my_detail_pref', 'detail_key', 'article_id');
ctx_ddl.set_attribute('my_detail_pref', 'detail_lineno', 'seq');
ctx_ddl.set_attribute('my_detail_pref', 'detail_text', 'text');

end;

Master/Detail Index Example

To index the document defined in this master/detail relationship, you specify a column in the master table with CREATE INDEX. The column you specify must be one of the allowable types.

This example uses the body column, whose function is to allow the creation of the master/detail index and to improve readability of the code. The my_detail_pref preference is set to DETAIL_DATASTORE with the required attributes:

CREATE INDEX myindex on my_master(body) indextype is ctxsys.context 
parameters('datastore my_detail_pref');

In this example, you can also specify the title or author column to create the index. However, if you do so, changes to these columns will trigger a re-index operation.

FILE_DATASTORE

The FILE_DATASTORE type is used for text stored in files accessed through the local file system.

FILE_DATASTORE has the following attribute(s):

Attribute	Attribute Values
path	path1:path2: :pathn

path

Specify the full directory path name of the files stored externally in a file system. When you specify the full directory path as such, you need only include file names in your text column.

You can specify multiple paths for path, with each path separated by a colon (:). File names are stored in the text column in the text table.

If you do not specify a path for external files with this attribute, Oracle requires that the path be included in the file names stored in the text column.

FILE_DATASTORE Example

This example creates a file datastore preference called COMMON_DIR that has a path of /mydocs:

begin
 ctx_ddl.create_preference('COMMON_DIR','FILE_DATASTORE');
 ctx_ddl.set_attribute('COMMON_DIR','PATH','/mydocs');
end;

When you populate the table mytable, you need only insert filenames. The path attribute tells the system where to look during the indexing operation.

create table mytable(id number primary key, docs varchar2(2000)); 
insert into mytable values(111555,'first.txt');
insert into mytable values(111556,'second.txt');
commit;

Create the index as follows:

create index myindex on mytable(docs)
  indextype is ctxsys.context
  parameters ('datastore COMMON_DIR'); 

URL_DATASTORE

Use the URL_DATASTORE type for text stored:

• In files on the World Wide Web (accessed through HTTP or FTP)
• In files in the local file system (accessed through the file protocol)

You store each URL in a single text field.

URL Syntax

The syntax of a URL you store in a text field is as follows (with brackets indicating optional parameters):

[URL:]<access_scheme>://<host_name>[:<port_number>]/[<url_path>]

The access_scheme string you specify can be either ftp, http, or file. For example:

http://mymachine.us.oracle.com/home.html

As this syntax is partially compliant with the RFC 1738 specification, the following restriction holds for the URL syntax:

• The URL must contain only printable ASCII characters. Nonprintable ASCII characters and multibyte characters must be escaped with the %xx notation, where xx is the hexadecimal representation of the special character.

  Note: The login:password@ syntax within the URL is supported only for the ftp access scheme.

URL_DATASTORE Attributes

URL_DATASTORE has the following attributes:

Attribute	Attribute Values
timeout	Specify the timeout in seconds. The valid range is 15 to 3600 seconds. The default is 30.
maxthreads	Specify the maximum number of threads that can be running simultaneously. Use a number between 1and 1024. The default is 8.
urlsize	Specify the maximum length of URL string in bytes. Use a number between 32 and 65535. The default is 256.
maxurls	Specify maximum size of URL buffer. Use a number between 32 and 65535. The defaults is 256.
maxdocsize	Specify the maximum document size. Use a number between 256 and 2,147,483,647 bytes (2 gigabytes). The defaults is 2,000,000.
http_proxy	Specify the host name of http proxy server. Optionally specify port number with a colon in the form hostname:port.
ftp_proxy	Specify the host name of ftp proxy server. Optionally specify port number with a colon in the form hostname:port.
no_proxy	Specify the domain for no proxy server. Use a comma separated string of up to 16 domain names.

timeout

Specify the length of time, in seconds, that a network operation such as a connect or read waits before timing out and returning a timeout error to the application. The valid range for timeout is 15 to 3600 and the default is 30.

maxthreads

Specify the maximum number of threads that can be running at the same time. The valid range for maxthreads is 1 to 1024 and the default is 8.

urlsize

Specify the maximum length, in bytes, that the URL data store supports for URLs stored in the database. If a URL is over the maximum length, an error is returned. The valid range for urlsize is 32 to 65535 and the default is 256.

maxurls

Specify the maximum number of rows that the internal buffer can hold for HTML documents (rows) retrieved from the text table. The valid range for maxurls is 32 to 65535 and the default is 256.

Specify the maximum size, in bytes, that the URL datastore supports for accessing HTML documents whose URLs are stored in the database. The valid range for maxdocsize is 1 to 2,147,483,647 (2 gigabytes), and the default is 2,000,000.

http_proxy

Specify the fully qualified name of the host machine that serves as the HTTP proxy (gateway) for the machine on which Oracle Text is installed. You can optionally specify port number with a colon in the form hostname:port.

You must set this attribute if the machine is in an intranet that requires authentication through a proxy server to access Web files located outside the firewall.

ftp_proxy

Specify the fully-qualified name of the host machine that serves as the FTP proxy (gateway) for the machine on which Oracle Text is installed. You can optionally specify a port number with a colon in the form hostname:port.

This attribute must be set if the machine is in an intranet that requires authentication through a proxy server to access Web files located outside the firewall.

no_proxy

Specify a string of domains (up to sixteen, separate by commas) which are found in most, if not all, of the machines in your intranet. When one of the domains is encountered in a host name, no request is sent to the machine(s) specified for ftp_proxy and http_proxy. Instead, the request is processed directly by the host machine identified in the URL.

For example, if the string us.oracle.com, uk.oracle.com is entered for no_proxy, any URL requests to machines that contain either of these domains in their host names are not processed by your proxy server(s).

URL_DATASTORE Example

This example creates a URL_DATASTORE preference called URL_PREF for which the http_proxy, no_proxy, and timeout attributes are set. The defaults are used for the attributes that are not set.

begin
 ctx_ddl.create_preference('URL_PREF','URL_DATASTORE');
 ctx_ddl.set_attribute('URL_PREF','HTTP_PROXY','www-proxy.us.oracle.com');
 ctx_ddl.set_attribute('URL_PREF','NO_PROXY','us.oracle.com');
 ctx_ddl.set_attribute('URL_PREF','Timeout','300');
end;

Create the table and insert values into it:

create table urls(id number primary key, docs varchar2(2000));
insert into urls values(111555,'http://context.us.oracle.com');
insert into urls values(111556,'http://www.sun.com');
commit;
 

To create the index, specify URL_PREF as the datastore:

create index datastores_text on urls ( docs ) 
  indextype is ctxsys.context 
  parameters ( 'Datastore URL_PREF' ); 

USER_DATASTORE

Use the USER_DATASTORE type to define stored procedures that synthesize documents during indexing. For example, a user procedure might synthesize author, date, and text columns into one document to have the author and date information be part of the indexed text.

The USER_DATASTORE has the following attributes:

Attribute	Attribute Value
procedure	Specify the procedure that synthesizes the document to be indexed. This procedure must be owned by CTXSYS and must be executable by the index owner.
output_type	Specify the data type of the second argument to procedure. Valid values are CLOB, BLOB, CLOB_LOC, BLOB_LOC, or VARCHAR2. The default is CLOB. When you specify CLOB_LOC, BLOB_LOC, you indicate that no temporary CLOB or BLOB is needed, since your procedure copies a locator to the IN/OUT second parameter.

procedure

Specify the name of the procedure that synthesizes the document to be indexed. This specification must be in the form PROCEDURENAME or PACKAGENAME.PROCEDURENAME. The schema owner name is constrained to CTXSYS, so specifying owner name is not necessary.

The procedure you specify must have two arguments defined as follows:

procedure (r IN ROWID, c IN OUT NOCOPY <output_type>)

The first argument r must be of type ROWID. The second argument c must be of type output_type. NOCOPY is a compiler hint that instructs Oracle to pass parameter c by reference if possible.

The stored procedure is called once for each row indexed. Given the rowid of the current row, procedure must write the text of the document into its second argument, whose type you specify with output_type.

Constraints

The following constraints apply to procedure:

• procedure must be owned by CTXSYS
• procedure must be executable by the index owner
• procedure cannot issue DDL or transaction control statements like COMMIT

Editing Procedure after Indexing

If you change or edit the stored procedure, indexes based upon it will not be notified, so you must manually re-create such indexes. So if the stored procedure makes use of other columns, and those column values change, the row will not be re-indexed. The row is re-indexed only when the indexed column changes.

output_type

Specify the datatype of the second argument to procedure. You can use either CLOB, BLOB, CLOB_LOC, BLOB_LOC, or VARCHAR2.

USER_DATASTORE with CLOB Example

Consider a table in which the author, title, and text fields are separate, as in the articles table defined as follows:

create table articles( 
    id       number, 
    author   varchar2(80), 
    title    varchar2(120), 
    text     clob );

The author and title fields are to be part of the indexed document text. Assume user appowner writes a stored procedure with the user datastore interface that synthesizes a document from the text, author, and title fields:

create procedure myproc(rid in rowid, tlob in out clob) is 
  begin 
      for c1 in (select author, title, text from articles 
                  where rowid = rid) 
      loop 


   dbms_lob.writeappend(tlob, length(c1.title), c1.title);
   dbms_lob.writeappend(tlob, length(c1.author), c1.author);
   dbms_lob.writeappend(tlob, length(c1.text), c1.text);

end loop; end;

This procedure takes in a rowid and a temporary CLOB locator, and concatenates all the article's columns into the temporary CLOB. The for loop executes only once.

Only procedures owned by CTXSYS are allowed for the user datastore. Therefore, CTXSYS must wrap the user procedure (owned by appowner) with a CTXSYS owned procedure as follows:

create procedure s_myproc(rid in rowid, tlob in out clob) is 
 begin 
      appowner.myproc(rid, tlob); 
 end; 
 

The CTXSYS user must make sure that the index owner can execute the stub procedure by granting execute privileges as follows:

grant execute on s_myproc to appowner ;
 

The user appowner creates the preference, setting the procedure attribute to the name of the ctxsys stub procedure as follows:

begin


ctx_ddl.create_preference('myud', 'user_datastore'); 
ctx_ddl.set_attribute('myud', 'procedure', 's_myproc'); 
ctx_ddl.set_attribute('myud', 'output_type', 'CLOB'); 

end;

When appowner creates the index on articles(text) using this preference, the indexing operation sees author and title in the document text.

USER_DATASTORE with BLOB_LOC Example

The following procedure might be used with OUTPUT_TYPE BLOB_LOC:

procedure myds(rid in rowid, dataout in out nocopy blob)
is
  l_dtype varchar2(10);
  l_pk    number;
begin
  select dtype, pk into l_dtype, l_pk from mytable where rowid = rid;
  if (l_dtype = 'MOVIE') then
    select movie_data into dataout from movietab where fk = l_pk;
  elsif (l_dtype = 'SOUND') then
    select sound_data into dataout from soundtab where fk = l_pk;
  end if;
end;

Because only procedures owned by CTXSYS are allowed for the user datastore, CTXSYS must wrap the user procedure (owned by appowner) with a CTXSYS owned procedure as follows:

create procedure s_myproc(rid in rowid, tlob in out blob) is 
 begin 
      appowner.myds(rid, tlob); 
 end; 
 

The CTXSYS user must make sure that the index owner can execute the stub procedure by granting execute privileges as follows:

grant execute on s_myproc to appowner ;
 

The user appowner creates the preference, setting the procedure and output_type attributes to correspond to the ctxsys stub procedure as follows:

begin


ctx_ddl.create_preference('myud', 'user_datastore'); 
ctx_ddl.set_attribute('myud', 'procedure', 's_myproc'); 
ctx_ddl.set_attribute('myud', 'output_type', 'blob_loc'); 

end;

NESTED_DATASTORE

Use the nested datastore type to index documents stored as rows in a nested table.

Attribute	Attribute Value
nested_column	Specify the name of the nested table column.This attribute is required. Specify only the column name. Do not specify schema owner or containing table name.
nested_type	Specify the type of nested table. This attribute is required. You must provide owner name and type.
nested_lineno	Specify the name of the attribute in the nested table that orders the lines. This is like DETAIL_LINENO in detail datastore. This attribute is required.
nested_text	Specify the name of the column in the nested table type that contains the text of the line. This is like DETAIL_TEXT in detail datastore. This attribute is required. LONG column types are not supported as nested table text columns.
binary	Specify FALSE for Oracle to automatically insert a new line between lines when synthesizing the document text. If you specify TRUE, Oracle does not do this. This attribute is not required. The default is FALSE.

When using the nested table datastore, you must index a dummy column, because the extensible indexing framework disallows indexing the nested table column. See the example.

DML on the nested table is not automatically propagated to the dummy column used for indexing. For DML on the nested table to be propagated to the dummy column, your application code or trigger must explicitly update the dummy column.

Filter defaults for the index are based on the type of the nested_text column.

During validation, Oracle checks that the type exists and that the attributes you specify for nested_lineno and nested_text exist in the nested table type. Oracle does not check that the named nested table column exists in the indexed table.

NESTED_DATASTORE Example

Create the Nested Table

The following code creates a nested table and a storage table mytab for the nested table:

create type nt_rec as object (
  lno number, -- line number
  ltxt varchar2(80) -- text of line
);

create type nt_tab as table of nt_rec;
create table mytab (
   id number primary key, -- primary key
   dummy char(1), -- dummy column for indexing
   doc nt_tab -- nested table
)
nested table doc store as myntab;

Insert Values into Nested Table

The following code inserts values into the nested table for the parent row with id equal to 1.

insert into mytab values (1, null, nt_tab());
insert into table(select doc from mytab where id=1) values (1, 'the dog');
insert into table(select doc from mytab where id=1) values (2, 'sat on mat ');
commit;

Create Nested Table Preferences

The following code sets the preferences and attributes for the NESTED_DATASTORE according to the definitions of the nested table type nt_tab and the parent table mytab:

begin
-- create nested datastore pref
ctx_ddl.create_preference('ntds','nested_datastore'); 

-- nest tab column in main table
ctx_ddl.set_attribute('ntds','nested_column', 'doc'); 

-- nested table type
ctx_ddl.set_attribute('ntds','nested_type', 'scott.nt_tab');

-- lineno column in nested table
ctx_ddl.set_attribute('ntds','nested_lineno','lno');

--text column in nested table
ctx_ddl.set_attribute('ntds','nested_text', 'ltxt');
end;

Create Index on Nested Table

The following code creates the index using the nested table datastore:

create index myidx on mytab(dummy) -- index dummy column, not nest table
indextype is ctxsys.context parameters ('datastore ntds');

Query Nested Datastore

The following select statement queries the index built from a nested table:

select * from mytab where contains(dummy, 'dog and mat')>0;
-- returns document 1, since it has dog in line 1 and mat in line 2.

Filter Types

Use the filter types to create preferences that determine how text is filtered for indexing. Filters allow word processor and formatted documents as well as plain text, HTML, and XML documents to be indexed.

For formatted documents, Oracle stores documents in their native format and uses filters to build temporary plain text or HTML versions of the documents. Oracle indexes the words derived from the plain text or HTML version of the formatted document.

To create a filter preference, you must use one of the following types:

Filter Preference type	Description
CHARSET_FILTER	Character set converting filter
INSO_FILTER	Inso filter for filtering formatted documents
NULL_FILTER	No filtering required. Use for indexing plain text, HTML, or XML documents
USER_FILTER	User-defined external filter to be used for custom filtering
PROCEDURE_FILTER	User-defined stored procedure filter to be used for custom filtering.

CHARSET_FILTER

Use the CHARSET_FILTER to convert documents from a non-database character set to the database character set.

CHARSET_FILTER has the following attribute:

Attribute

Attribute Value

charset

Specify the Globalization Support name of source character set. If you specify UTF16AUTO, this filter automatically detects the if the character set is UTF16 big- or little-endian. Specify JAAUTO for Japanese character set auto-detection. This filter automatically detects the custom character specification in JA16EUC or JA16SJIS and converts to the database character set. This filter is useful in Japanese when your data files have mixed character sets.

UTF-16 Big- and Little-Endian Detection

If your character set is UTF-16, you can specify UTF16AUTO to automatically detect big- or little-endian data. Oracle does so by examining the first two bytes of the document row.

If the first two bytes are 0xFE, 0xFF, the document is recognized as little-endian and the remainder of the document minus those two bytes is passed on for indexing.

If the first two bytes are 0xFF, 0xFE, the document is recognized as big-endian and the remainder of the document minus those two bytes is passed on for indexing.

If the first two bytes are anything else, the document is assumed to be big-endian and the whole document including the first two bytes is passed on for indexing.

Indexing Mixed-Character Set Columns

A mixed character set column is one that stores documents of different character sets. For example, a text table might store some documents in WE8ISO8859P1 and others in UTF8.

To index a table of documents in different character sets, you must create your base table with a character set column. In this column, you specify the document character set on a per-row basis. To index the documents, Oracle converts the documents into the database character set.

Character set conversion works with the CHARSET_FILTER. When the charset column is NULL or not recognized, Oracle assumes the source character set is the one specified in the charset attribute.

Indexing Mixed-Character Set Example

For example, create the table with a charset column:

create table hdocs (
     id number primary key,
     fmt varchar2(10),
     cset varchar2(20),
     text varchar2(80)
);

Insert plain-text documents and name the character set:

insert into hdocs values(1, 'text', 'WE8ISO8859P1', '/docs/iso.txt');
insert in hdocs values (2, 'text', 'UTF8', '/docs/utf8.txt');
commit;

Create the index and name the charset column:

create index hdocsx on hdocs(text) indextype is ctxsys.context
  parameters ('datastore ctxsys.file_datastore 
  filter ctxsys.charset_filter 
  format column fmt
  charset column cset');

INSO_FILTER

The INSO_FILTER is a universal filter that filters most document formats. This filtering technology is licensed from Stellent Chicago, Inc.

Use it for indexing single and mixed-format columns.

The INSO_FILTER has the following attribute:

Attribute	Attribute Values
timeout	Specify the INSO_FILTER timeout in seconds. Use a number between 0 and 42,949,672. Default is 120. Setting this value 0 disables the feature. How this wait period is used depends on how you set timeout_type. This feature is disabled for rows for which the corresponding charset and format column cause the INSO_FILTER to bypass the row, such as when format is marked TEXT. Use this feature to prevent the Oracle indexing operation from waiting indefinitely on a hanging Inso filter operation.
timeout_type	Specify either HEURISTIC or FIXED. Default is HEURISTIC. Specify HEURISTIC for Oracle to check every TIMEOUT seconds if output from Output in HTML Export has increased. The operation terminates for the document if output has not increased. An error is recorded in the CTX_USER_INDEX_ERRORS view and Oracle moves to the next document row to be indexed. Specify FIXED to terminate the Outside In HTML Export processing after TIMEOUT seconds regardless of whether filtering was progressing normally or just hanging. This value is useful when indexing throughput is more important than taking the time to successfully filter large documents.

Indexing Formatted Documents

To index a text column containing formatted documents such as Microsoft Word, use the INSO_FILTER. This filter automatically detects the document format. You can use the CTXSYS.INSO_FILTER system-defined preference in the parameter clause as follows:

create index hdocsx on hdocs(text) indextype is ctxsys.context
  parameters ('datastore ctxsys.file_datastore 
  filter ctxsys.inso_filter');

Bypassing Plain Text or HTML in Mixed Format Columns

A mixed-format column is a text column containing more than one document format, such as a column that contains Microsoft Word, PDF, plain text, and HTML documents.

The INSO_FILTER can index mixed-format columns. However, you might want to have the INSO filter bypass the plain text or HTML documents. Filtering plain text or HTML with the INSO_FILTER is redundant.

The format column in the base table allows you to specify the type of document contained in the text column. The only two types you can specify are TEXT and BINARY. During indexing, the INSO_FILTER ignores any document typed TEXT (assuming the charset column is not specified.)

To set up the INSO_FILTER bypass mechanism, you must create a format column in your base table.

For example:

create table hdocs (
     id number primary key,
     fmt varchar2(10),
     text varchar2(80)
);

Assuming you are indexing mostly Word documents, you specify BINARY in the format column to filter the Word documents. Alternatively, to have the INSO_FILTER ignore an HTML document, specify TEXT in the format column.

For example, the following statements add two documents to the text table, assigning one format as BINARY and the other TEXT:

insert into hdocs values(1, 'binary', '/docs/myword.doc');
insert in hdocs values (2, 'text', '/docs/index.html');
commit;

To create the index, use CREATE INDEX and specify the format column name in the parameter string:

create index hdocsx on hdocs(text) indextype is ctxsys.context
  parameters ('datastore ctxsys.file_datastore 
  filter ctxsys.inso_filter 
  format column fmt');

If you do not specify TEXT or BINARY for the format column, BINARY is used.

Character Set Conversion With Inso

The INSO_FILTER converts documents to the database character set when the document format column is set to TEXT. In this case, the INSO_FILTER looks at the charset column to determine the document character set.

If the charset column value is not an Oracle character set name, the document is passed through without any character set conversion.

If you do specify the charset column and do not specify the format column, the INSO_FILTER works like the CHARSET_FILTER, except that in this case there is no Japanese character set auto-detection.

Plain Text Indexing and the INSO_FILTER

Oracle does not recommend using INSO_FILTER to index plain text documents.

If your table contains text documents exclusively, use the NULL_FILTER or the USER_FILTER.

If your table contains text documents mixed with formatted documents, Oracle recommends creating a format column and marking the text documents as TEXT to bypass INSO_FILTER. In such cases, Oracle also recommends creating a charset column to indicate the document character set.

However, if you use INSO_FILTER to index nonbinary (text) documents and you specify no format column and no charset column, the INSO_FILTER processes the document. Your indexing process is thus subject to the character set limitations of Inso technology. Specifically, your application must ensure that one of the following conditions is true:

• The document character set is the same as the database character set and the database character set is one of the following:
  • US7ASCII
  • WE8ISO8859P1
  • JA16SJIS
  • KO16KSC5601
  • ZHS16CGB231280
  • ZHT16BIG5
• The database character set is none of those listed and the document is in the WE8ISO8859P1 character set.

NULL_FILTER

Use the NULL_FILTER type when plain text or HTML is to be indexed and no filtering needs to be performed. NULL_FILTER has no attributes.

Indexing HTML Documents

If your document set is entirely HTML, Oracle recommends that you use the NULL_FILTER in your filter preference.

For example, to index an HTML document set, you can specify the system-defined preferences for NULL_FILTER and HTML_SECTION_GROUP as follows:

create index myindex on docs(htmlfile) indextype is ctxsys.context 
  parameters('filter ctxsys.null_filter
  section group ctxsys.html_section_group');

USER_FILTER

Use the USER_FILTER type to specify an external filter for filtering documents in a column. USER_FILTER has the following attribute:

Attribute	Attribute Values
command	Specify the name of the filter executable.

command

Specify the executable for the single external filter used to filter all text stored in a column. If more than one document format is stored in the column, the external filter specified for command must recognize and handle all such formats.

The executable you specify must exist in the $ORACLE_HOME/ctx/bin directory. You must create your user-filter executable with two parameters: the first is the name of the input file to be read, and the second is the name of the output file to be written to.

If all the document formats are supported by INSO_FILTER, use INSO_FILTER instead of USER_FILTER unless additional tasks besides filtering are required for the documents.

User Filter Example

The following example perl script to be used as the user filter. This script converts the input text file specified in the first argument to uppercase and writes the output to the location specified in the second argument:

#!/usr/local/bin/perl

open(IN, $ARGV[0]);
open(OUT, ">".$ARGV[1]);

while (<IN>)
{
  tr/a-z/A-Z/;
  print OUT;
}

close (IN);
close (OUT);

Assuming that this file is named upcase.pl, create the filter preference as follows:

begin 
  ctx_ddl.create_preference 
    ( 
      preference_name => 'USER_FILTER_PREF', 
      object_name     => 'USER_FILTER' 
    ); 
  ctx_ddl.set_attribute
    ('USER_FILTER_PREF','COMMAND','upcase.pl');
end; 

Create the index in SQL*Plus as follows:

create index user_filter_idx on user_filter ( docs ) 
  indextype is ctxsys.context 
  parameters ('FILTER USER_FILTER_PREF'); 

PROCEDURE_FILTER

Use the PROCEDURE_FILTER type to filter your documents with a stored procedure. The stored procedure is called each time a document needs to be filtered.

This type has the following attributes:

Attribute	Purpose	Allowable Values
procedure	Name of the filter stored procedure.	Any CTXSYS owned procedure. The procedure can be a PL/SQL stored procedure.
input_type	Type of input argument for stored procedure.	VARCHAR2, BLOB, CLOB, FILE
output_type	Type of output argument for stored procedure.	VARCHAR2, CLOB, FILE
rowid_parameter	Include rowid parameter?	TRUE/FALSE
format_parameter	Include format parameter?	TRUE/FALSE
charset_parameter	Include charset parameter?	TRUE/FALSE

procedure

Specify the name of the stored procedure to use for filtering. The procedure can be a PL/SQL stored procedure. The procedure can be a safe callout or call a safe callout.

The procedure must be owned by CTXSYS and have one of the following signatures:

PROCEDURE(IN BLOB, IN OUT NOCOPY CLOB)
PROCEDURE(IN CLOB, IN OUT NOCOPY CLOB)
PROCEDURE(IN VARCHAR, IN OUT NOCOPY CLOB)
PROCEDURE(IN BLOB, IN OUT NOCOPY VARCHAR2)
PROCEDURE(IN CLOB, IN OUT NOCOPY VARCHAR2)
PROCEDURE(IN VARCHAR2, IN OUT NOCOPY VARCHAR2)
PROCEDURE(IN BLOB, IN VARCHAR2)
PROCEDURE(IN CLOB, IN VARCHAR2)
PROCEDURE(IN VARCHAR2, IN VARCHAR2)

The first argument is the content of the unfiltered row as passed out by the datastore. The second argument is for the procedure to pass back the filtered document text.

The procedure attribute is mandatory and has no default.

input_type

Specify the type of the input argument of the filter procedure. You can specify one of the following:

Type	Description
BLOB	The input argument is of type BLOB. The unfiltered document is contained in the BLOB passed in.
CLOB	The input argument is of type CLOB. The unfiltered document is contained in the CLOB passed in. No pre-filtering or character set conversion is done. If the datastore outputs binary data, that binary data is written directly to the CLOB, with Globalization Support doing implicit mapping to character data as best it can.
VARCHAR2	The input argument is of type VARCHAR2. The unfiltered document is contained in the VARCHAR2 passed in. The document can be a maximum of 32767 bytes of data. If the unfiltered document is greater than this length, an error is raised for the document and the filter procedure is not called.
FILE	The input argument is of type VARCHAR2. The unfiltered document content is contained in a temporary file in the file system whose filename is stored in the VARCHAR2 passed in. For example, the value of the passed-in VARCHAR2 might be 'tmp/mydoc.tmp' which means that the document content is stored in the file '/tmp/mydoc.tmp'. The file input type is useful only when your procedure is a safe callout, which can read the file.

The input_type attribute is not mandatory. If not specified, BLOB is the default.

output_type

Specify the type of output argument of the filter procedure. You can specify one of the following types:

Type	Description
CLOB	The output argument is IN OUT NOCOPY CLOB. Your procedure must write the filtered content to the CLOB passed in.
VARCHAR2	The output argument is IN OUT NOCOPY VARCHAR2. Your procedure must write the filtered content to the VARCHAR2 variable passed in.
FILE	The output argument must be IN VARCHAR2. On entering the filter procedure, the output argument is the name of a temporary file. The filter procedure must write the filtered contents to this named file. Using a FILE output type is useful only when the procedure is a safe callout, which can write to the file.

The output_type attribute is not mandatory. If not specified, CLOB is the default.

rowid_ parameter

When you specify TRUE, the rowid of the document to be filtered is passed as the first parameter, before the input and output parameters.

For example, with INPUT_TYPE BLOB, OUTPUT_TYPE CLOB, and ROWID_PARAMETER TRUE, the filter procedure must have the signature as follows:

procedure(in rowid, in blob, in out nocopy clob)

This attribute is useful for when your procedure requires data from other columns or tables. This attribute is not mandatory. The default is FALSE.

format_parameter

When you specify TRUE, the value of the format column of the document being filtered is passed to the filter procedure before input and output parameters, but after the rowid parameter, if enabled.

You specify the name of the format column at index time in the parameters string, using the keyword 'format column <columnname>'. The parameter type must be IN VARCHAR2.

The format column value can be read via the rowid parameter, but this attribute allows a single filter to work on multiple table structures, because the format attribute is abstracted and does not require the knowledge of the name of the table or format column.

FORMAT_PARAMETER is not mandatory. The default is FALSE.

charset_parameter

When you specify TRUE, the value of the charset column of the document being filtered is passed to the filter procedure before input and output parameters, but after the rowid and format parameter, if enabled.

You specify the name of the charset column at index time in the parameters string, using the keyword 'charset column <columnname>'. The parameter type must be IN VARCHAR2.

CHARSET_PARAMETER attribute is not mandatory. The default is FALSE.

Parameter Order

ROWID_PARAMETER, FORMAT_PARAMETER, and CHARSET_PARAMETER are all independent. The order is rowid, the format, then charset, but the filter procedure is passed only the minimum parameters required.

For example, assume that INPUT_TYPE is BLOB and OUTPUT_TYPE is CLOB. If your filter procedure requires all parameters, the procedure signature must be:

(id IN ROWID, format IN VARCHAR2, charset IN VARCHAR2, input IN BLOB, output IN 
OUT NOCOPY CLOB)

If your procedure requires only the ROWID, then the procedure signature must be:

(id IN ROWID,input IN BLOB, ouput IN OUT NOCOPY CLOB)

Create Index Requirements

In order to create an index using a PROCEDURE_FILTER preference, the index owner must have execute permission on the procedure.Oracle checks this at index time, which is similar to the security measures for USER_DATASTORE.

Error Handling

The filter procedure can raise any errors needed through the normal PL/SQL raise_application_error facility. These errors are propagated to the CTX_USER_INDEX_ERRORS view or reported to the user, depending on how the filter is invoked.

Procedure Filter Preference Example

Consider a filter procedure CTXSYS.NORMALIZE that you define with the following signature:

PROCEDURE NORMALIZE(id IN ROWID, charset IN VARCHAR2, input IN CLOB, 
output IN OUT NOCOPY VARCHAR2);

To use this procedure as your filter, set up your filter preference as follows:

begin
ctx_ddl.create_preference('myfilt', 'procedure_filter');
ctx_ddl.set_attribute('myfilt', 'procedure', 'normalize');
ctx_ddl.set_attribute('myfilt', 'input_type', 'clob');
ctx_ddl.set_attribute('myfilt', 'output_type', 'varchar2');
ctx_ddl.set_attribute('myfilt', 'rowid_parameter', 'TRUE');
ctx_ddl.set_attribute('myfilt', 'charset_parameter', 'TRUE');
end;

Lexer Types

Use the lexer preference to specify the language of the text to be indexed. To create a lexer preference, you must use one of the following lexer types:

type	Description
BASIC_LEXER	Lexer for extracting tokens from text in languages, such as English and most western European languages that use white space delimited words.
MULTI_LEXER	Lexer for indexing tables containing documents of different languages
CHINESE_VGRAM_LEXER	Lexer for extracting tokens from Chinese text.
CHINESE_LEXER	Lexer for extracting tokens from Chinese text.
JAPANESE_VGRAM_LEXER	Lexer for extracting tokens from Japanese text.
JAPANESE_LEXER	Lexer for extracting tokens from Japanese text.
KOREAN_LEXER	Lexer for extracting tokens from Korean text.
KOREAN_MORPH_LEXER	Lexer for extracting tokens from Korean text (recommended).
USER_LEXER	Lexer you create to index a particular language.

BASIC_LEXER

Use the BASIC_LEXER type to identify tokens for creating Text indexes for English and all other supported whitespace delimited languages.

The BASIC_LEXER also enables base-letter conversion, composite word indexing, case-sensitive indexing and alternate spelling for whitespace delimited languages that have extended character sets.

In English and French, you can use the BASIC_LEXER to enable theme indexing.

BASIC_LEXER supports any database character set.

BASIC_LEXER has the following attributes:

Attribute	Attribute Values
continuation	characters
numgroup	characters
numjoin	characters
printjoins	characters
punctuations	characters
skipjoins	characters
startjoins	non alphanumeric characters that occur at the beginning of a token (string)
endjoins	non alphanumeric characters that occur at the end of a token (string)
whitespace	characters (string)
newline	NEWLINE (\n) CARRIAGE_RETURN (\r)
base_letter	NO (disabled)
	YES (enabled)
mixed_case	NO (disabled)
	YES (enabled)
composite	DEFAULT (no composite word indexing, default)
	GERMAN (German composite word indexing)
	DUTCH (Dutch composite word indexing)
index_stems	0 NONE 1 ENGLISH 2 DERIVATIONAL 3 DUTCH 4 FRENCH 5 GERMAN 6 ITALIAN 7 SPANISH
index_themes	YES (enabled)
	NO (disabled, default)
index_text	YES (enabled, default
	NO (disabled)
prove_themes	YES (enabled, default)
	NO (disabled)
theme_language	AUTO (default)
	(any Globalization Support language)
alternate_spelling	GERMAN (German alternate spelling)
	DANISH (Danish alternate spelling)
	SWEDISH (Swedish alternate spelling)
	NONE (No alternate spelling, default)

continuation

Specify the characters that indicate a word continues on the next line and should be indexed as a single token. The most common continuation characters are hyphen '-' and backslash '\'.

numgroup

Specify a single character that, when it appears in a string of digits, indicates that the digits are groupings within a larger single unit.

For example, comma ',' might be defined as a numgroup character because it often indicates a grouping of thousands when it appears in a string of digits.

numjoin

Specify the characters that, when they appear in a string of digits, cause Oracle to index the string of digits as a single unit or word.

For example, period '.' can be defined as numjoin characters because it often serves as decimal points when it appears in a string of digits.

printjoins

Specify the non alphanumeric characters that, when they appear anywhere in a word (beginning, middle, or end), are processed as alphanumeric and included with the token in the Text index. This includes printjoins that occur consecutively.

For example, if the hyphen '-' and underscore '_' characters are defined as printjoins, terms such as pseudo-intellectual and _file_ are stored in the Text index as pseudo-intellectual and _file_.

punctuations

Specify the non-alphanumeric characters that, when they appear at the end of a word, indicate the end of a sentence. The defaults are period '.', question mark '?', and exclamation point '!'.

Characters that are defined as punctuations are removed from a token before text indexing. However, if a punctuations character is also defined as a printjoins character, the character is removed only when it is the last character in the token and it is immediately preceded by the same character.

For example, if the period (.) is defined as both a printjoins and a punctuations character, the following transformations take place during indexing and querying as well:

Token	Indexed Token
.doc	.doc
dog.doc	dog.doc
dog..doc	dog..doc
dog.	dog
dog...	dog..

In addition, BASIC_LEXER uses punctuations characters in conjunction with newline and whitespace characters to determine sentence and paragraph deliminters for sentence/paragraph searching.

skipjoins

Specify the non-alphanumeric characters that, when they appear within a word, identify the word as a single token; however, the characters are not stored with the token in the Text index.

For example, if the hyphen character '-' is defined as a skipjoins, the word pseudo-intellectual is stored in the Text index as pseudointellectual.

startjoins/endjoins

For startjoins, specify the characters that when encountered as the first character in a token explicitly identify the start of the token. The character, as well as any other startjoins characters that immediately follow it, is included in the Text index entry for the token. In addition, the first startjoins character in a string of startjoins characters implicitly ends the previous token.

For endjoins, specify the characters that when encountered as the last character in a token explicitly identify the end of the token. The character, as well as any other startjoins characters that immediately follow it, is included in the Text index entry for the token.

The following rules apply to both startjoins and endjoins:

• The characters specified for startjoins/endjoins cannot occur in any of the other attributes for BASIC_LEXER.
• startjoins/endjoins characters can occur only at the beginning or end of tokens

whitespace

Specify the characters that are treated as blank spaces between tokens. BASIC_LEXER uses whitespace characters in conjunction with punctuations and newline characters to identify character strings that serve as sentence delimiters for sentence and paragraph searching.

The predefined default values for whitespace are 'space' and 'tab'. These values cannot be changed. Specifying characters as whitespace characters adds to these defaults.

newline

Specify the characters that indicate the end of a line of text. BASIC_LEXER uses newline characters in conjunction with punctuations and whitespace characters to identify character strings that serve as paragraph delimiters for sentence and paragraph searching.

The only valid values for newline are NEWLINE and CARRIAGE_RETURN (for carriage returns). The default is NEWLINE.

base_letter

Specify whether characters that have diacritical marks (umlauts, cedillas, acute accents, and so on) are converted to their base form before being stored in the Text index. The default is NO (base-letter conversion disabled).

mixed_case

Specify whether the lexer leaves the tokens exactly as they appear in the text or converts the tokens to all uppercase. The default is NO (tokens are converted to all uppercase).

composite

Specify whether composite word indexing is disabled or enabled for either GERMAN or DUTCH text. The default is DEFAULT (composite word indexing disabled).

Words that are usually one entry in a German dictionary are not split into composite stems, while words that aren't dictionary entries are split into composite stems.

In order to retrieve the indexed composite stems, you must issue a stem query, such as $bahnhof. The language of the wordlist stemmer must match the language of the composite stems.

Stemming User-Dictionary

In your language, you can create a user dictionary to customize how words are decomposed.

You create the user dictionary in the $ORACLE_HOME/ctx/data/<language id> directory. The user dictionary must have the suffix .dct.

For example, the supplied user dictionary file for German is:

$ORACLE_HOME/ctx/data/del/drde.dct

The format for the user dictionary is as follows:

input term <tab> output term

The individual parts of the decomposed word must be separated by the # character. The following example entries are for the German word Hauptbahnhof:

Hauptbahnhof<tab>Haupt#Bahnhof
Hauptbahnhofes<tab>Haupt#Bahnhof
Hauptbahnhof<tab>Haupt#Bahnhof
Hauptbahnhoefe<tab>Haupt#Bahnhof

index_themes

Specify YES to index theme information in English or French. This makes ABOUT queries more precise. The index_themes and index_text attributes cannot both be NO.

If you use the BASIC_LEXER and specify no value for index_themes, this attribute defaults to NO.

You can set this parameter to TRUE for any indextype including CTXCAT. To issue an ABOUT query with CATSEARCH, use the query template with CONTEXT grammar.

prove_themes

Specify YES to prove themes. Theme proving attempts to find related themes in a document. When no related themes are found, parent themes are eliminated from the document.

While theme proving is acceptable for large documents, short text descriptions with a few words rarely prove parent themes, resulting in poor recall performance with ABOUT queries.

Theme proving results in higher precision and less recall (less rows returned) for ABOUT queries. For higher recall in ABOUT queries and possibly less precision, you can disable theme proving. Default is YES.

The prove_themes attribute is supported for CONTEXT and CTXRULE indexes.

theme_language

Specify which knowledge base to use for theme generation when index_themes is set to YES. When index_themes is NO, setting this parameter has no effect on anything.

You can specify any Globalization Support language or AUTO. You must have a knowledge base for the language you specify. This release provides a knowledge base in only English and French. In other languages, you can create your own knowledge base.

The default is AUTO, which instructs the system to set this parameter according to the language of the environment.

index_stems

Specify the stemmer to use for stem indexing.Tokens are stemmed to a single base form at index time in addition to the normal forms. Indexing stems enables better query performance for stem ($) queries, such as $computed.

index_text

Specify YES to index word information. The index_themes and index_text attributes cannot both be NO.

The default is NO.

alternate_spelling

Specify either GERMAN, DANISH, or SWEDISH to enable the alternate spelling in one of these languages. Enabling alternate spelling allows you to query a word in any of its alternate forms.

By default, alternate spelling is enabled in all three languages. You can specify NONE for no alternate spelling.

BASIC_LEXER Example

The following example sets printjoin characters and disables theme indexing with the BASIC_LEXER:

begin
ctx_ddl.create_preference('mylex', 'BASIC_LEXER');
ctx_ddl.set_attribute('mylex', 'printjoins', '_-');
ctx_ddl.set_attribute ( 'mylex', 'index_themes', 'NO');
ctx_ddl.set_attribute ( 'mylex', 'index_text', 'YES'); 
end;

To create the index with no theme indexing and with printjoins characters set as described, issue the following statement:

create index myindex on mytable ( docs ) 
  indextype is ctxsys.context 
  parameters ( 'LEXER mylex' ); 

MULTI_LEXER

Use MULTI_LEXER to index text columns that contain documents of different languages. For example, you can use this lexer to index a text column that stores English, German, and Japanese documents.

This lexer has no attributes.

You must have a language column in your base table. To index multi-language tables, you specify the language column when you create the index.

You create a multi-lexer preference with the CTX_DDL.CREATE_PREFERENCE. You add language-specific lexers to the multi-lexer preference with the CTX_DDL.ADD_SUB_LEXER procedure.

During indexing, the MULTI_LEXER examines each row's language column value and switches in the language-specific lexer to process the document.

Multi-language Stoplists

When you use the MULTI_LEXER, you can also use a multi-language stoplist for indexing.

MULTI_LEXER Example

Create the multi-language table with a primary key, a text column, and a language column as follows:

create table globaldoc (
   doc_id number primary key,
   lang varchar2(3),
   text clob
);

Assume that the table holds mostly English documents, with the occasional German or Japanese document. To handle the three languages, you must create three sub-lexers, one for English, one for German, and one for Japanese:

ctx_ddl.create_preference('english_lexer','basic_lexer');
ctx_ddl.set_attribute('english_lexer','index_themes','yes');
ctx_ddl.set_attribute('english_lexer','theme_language','english');

ctx_ddl.create_preference('german_lexer','basic_lexer');
ctx_ddl.set_attribute('german_lexer','composite','german');
ctx_ddl.set_attribute('german_lexer','mixed_case','yes');
ctx_ddl.set_attribute('german_lexer','alternate_spelling','german');

ctx_ddl.create_preference('japanese_lexer','japanese_vgram_lexer');

Create the multi-lexer preference:

ctx_ddl.create_preference('global_lexer', 'multi_lexer');

Since the stored documents are mostly English, make the English lexer the default using CTX_DDL.ADD_SUB_LEXER:

ctx_ddl.add_sub_lexer('global_lexer','default','english_lexer');

Now add the German and Japanese lexers in their respective languages with CTX_DDL.ADD_SUB_LEXER procedure. Also assume that the language column is expressed in the standard ISO 639-2 language codes, so add those as alternate values.

ctx_ddl.add_sub_lexer('global_lexer','german','german_lexer','ger');
ctx_ddl.add_sub_lexer('global_lexer','japanese','japanese_lexer','jpn');

Now create the index globalx, specifying the multi-lexer preference and the language column in the parameter clause as follows:

create index globalx on globaldoc(text) indextype is ctxsys.context
parameters ('lexer global_lexer language column lang');

Querying Multi-Language Tables

At query time, the multi-lexer examines the language setting and uses the sub-lexer preference for that language to parse the query. If the language is not set, then the default lexer is used.

Otherwise, the query is parsed and run as usual. The index contains tokens from multiple languages, so such a query can return documents in several languages. To limit your query to a given language, use a structured clause on the language column.

CHINESE_VGRAM_LEXER

The CHINESE_VGRAM_LEXER type identifies tokens in Chinese text for creating Text indexes. It has no attributes.

You can use this lexer if your database character set is one of the following:

• ZHS16CGB231280
• ZHS16GBK
• ZHT32EUC
• ZHT16BIG5
• ZHT32TRIS
• ZHT16MSWIN950
• ZHT16HKSCS
• UTF8

CHINESE_LEXER

The CHINESE_LEXER type identifies tokens in traditional and simplified Chinese text for creating Text indexes. It has no attributes.

This lexer offers the following benefits over the CHINESE_VGRAM_LEXER:

• generates a smaller index
• better query response time
• generates real word tokens resulting in better query precision
• supports stop words

Because the CHINESE_LEXER uses a new algorithm to generate tokens, indexing time is longer than with CHINESE_VGRAM_LEXER.

You can use this lexer if your database character is one of the Chinese or Unicode character sets supported by Oracle.

JAPANESE_VGRAM_LEXER

The JAPANESE_VGRAM_LEXER type identifies tokens in Japanese for creating Text indexes. It has no attributes.

You can use this lexer if your database character set is one of the following:

• JA16SJIS
• JA16EUC
• UTF8

JAPANESE_LEXER

The JAPANESE_LEXER type identifies tokens in Japanese for creating Text indexes. It has no attributes.

This lexer offers the following benefits over the JAPANESE_VGRAM_LEXER:

• generates a smaller index
• better query response time
• generates real word tokens resulting in better query precision

Because the JAPANESE_LEXER uses a new algorithm to generate tokens, indexing time is longer than with JAPANESE_VGRAM_LEXER.

The JAPANESE_LEXER supports the following character sets:

• JA16SJIS
• JA16EUC
• UTF8

Japanese Lexer Example

When you specify JAPANESE_LEXER for creating text index, the JAPANESE_LEXER resolves a sentence into words.

For example, the following compound word (natural language institute)

Text description of the illustration jap_befo.gif

is indexed as three tokens:

Text description of the illustration jap_afte.gif

In order to resolve a sentence into words, the internal dictionary is referenced. When a word cannot be found in the internal dictionary, Oracle uses the JAPANESE_VGRAM_LEXER to resolve it.

KOREAN_LEXER

The KOREAN_LEXER type identifies tokens in Korean text for creating Text indexes.

You can use this lexer if your database character set is one of the following:

• KO16KSC5601
• UTF8

When you use the KOREAN_LEXER, you can specify the following boolean attributes:

Attribute	Attribute Values
verb	Specify TRUE or FALSE to index verbs. Default is TRUE.
adjective	Specify TRUE or FALSE to index adjectives. Default is TRUE.
adverb	Specify TRUE or FALSE to index adverb. Default is TRUE.
onechar	Specify TRUE or FALSE to index one character. Default is TRUE.
number	Specify TRUE or FALSE to index number. Default is TRUE.
udic	Specify TRUE or FALSE to index user dictionary. Default is TRUE.
xdic	Specify TRUE or FALSE to index x-user dictionary. Default is TRUE.
composite	Specify TRUE or FALSE to index composite words.
morpheme	Specify TRUE or FALSE for morphological analysis. Default is TRUE.
toupper	Specify TRUE or FALSE to convert English to uppercase. Default is TRUE.
tohangeul	Specify TRUE or FALSE to convert to hanga to hangeul. Default is TRUE.

Limitations

Sentence and paragraph sections are not supported with the Korean lexer.

KOREAN_MORPH_LEXER

The KOREAN_MORPH_LEXER type identifies tokens in Korean text for creating Oracle Text indexes. The KOREAN_MORPH_LEXER lexer offers the following benefits over KOREAN_LEXER:

• better morphological analysis of Korean text
• faster indexing
• smaller indexes
• more accurate query searching

Supplied Dictionaries

The KOREAN_MORPH_LEXER uses four dictionaries:

Dictionary	File
System	$ORACLE_HOME/ctx/data/kolx/drk2sdic.dat
Grammar	$ORACLE_HOME/ctx/data/kolx/drk2gram.dat
Stopword	$ORACLE_HOME/ctx/data/kolx/drk2xdic.dat
User-defined	$ORACLE_HOME/ctx/data/kolx/drk2udic.dat

The grammar, user-defined, and stopword dictionaries are text format KSC 5601. You can modify these dictionaries using the defined rules. The system dictionary must not be modified.

You can add unregistered words to the user-defined dictionary file. The rules for specifying new words are in the file.

Supported Character Sets

You can use KOREAN_MORPH_LEXER if your database character set is one of the following:

• KO16KSC5601
• UTF8

Attributes

When you use the KOREAN_MORPH_LEXER, you can specify the following attributes:

Attribute	Attribute Values
verb_adjective	Specify TRUE or FALSE to index verbs and adjectives. Default is FALSE.
one_char_word	Specify TRUE or FALSE to index one syllable. Default is FALSE.
number	Specify TRUE or FALSE to index number. Default is FALSE.
user_dic	Specify TRUE or FALSE to index user dictionary. Default is TRUE.
stop_dic	Specify TRUE of FALSE to use stop-word dictionary. Default is TRUE. The stop-word dictionary belongs to KOREAN_MORPH_LEXER.
composite	Specify indexing style of composite noun. Specify COMPOSITE_ONLY to index only composite nouns. Specify NGRAM to index all noun components of a composite noun. Specify COMPONENT_WORD to index single noun components of composite nouns as well as the composite noun itself. Default is COMPONENT_WORD. The example below describes the difference between NGRAM and COMPONENT_WORD.
morpheme	Specify TRUE or FALSE for morphological analysis. If set to FALSE, tokens are created from the words that are divided by delimiters such as white space in the document. Default is TRUE.
to_upper	Specify TRUE or FALSE to convert English to uppercase. Default is TRUE.
hanja	Specify TRUE to index hanja characters. If set to FALSE, hanja characters are converted to hangul characters. Default is FALSE.
long_word	Specify TRUE to index long words that have more than 16 syllables in Korean. Default is FALSE.
japanese	Specify TRUE to index Japanese characters in KSC5601 code. Default is FALSE.
english	Specify TRUE to index alphanumeric strings. Default is TRUE.

Limitations

Sentence and paragraph sections are not supported with the Korean lexer.

KOREAN_MORPH_LEXER Example: Setting Composite Attribute

You can use the composite attribute to control how composite nouns are indexed.

NGRAM Example

When you specify NGRAM for the composite attribute, composite nouns are indexed with all possible component tokens. For example, the following composite noun (information processing institute):

Text description of the illustration 1.jpg

is indexed as six tokens:

Text description of the illustration 2.jpg

Text description of the illustration 3.jpg

You can specify NGRAM indexing as follows:

begin
ctx_ddl.create_preference('korean_lexer','KOREAN_MORPH_LEXER');
ctx_ddl.set_attribute('korean_lexer','COMPOSITE','NGRAM');
end

To create the index:

create index koreanx on korean(text) indextype is ctxsys.context
parameters ('lexer korean_lexer');

COMPONENT_WORD Example

When you specify COMPONENT_WORD for the composite attribute, composite nouns and their components are indexed. For example, the following composite noun (information processing institute):

Text description of the illustration 1.jpg

is indexed as four tokens:

Text description of the illustration 1.jpg

Text description of the illustration comp.jpg

You can specify COMPONENT_WORD indexing as follows:

begin
ctx_ddl.create_preference('korean_lexer','KOREAN_MORPH_LEXER');
ctx_ddl.set_attribute('korean_lexer','COMPOSITE','COMPONENT_WORD');
end

To create the index:

create index koreanx on korean(text) indextype is ctxsys.context
parameters ('lexer korean_lexer');

USER_LEXER

Use USER_LEXER to plug in your own language specific lexing solution. This enables you to define lexers for languages that are not supported by Oracle Text or to define a new lexer for a language that is supported but inappropriate for your application.

The user-defined lexer you register with Oracle Text is composed of two routines that you must supply:

User-define Routine	Description
Indexing Procedure	Stored procedure (PL/SQL) which implements the tokenization of documents and stop words. Output must be an XML document as specified in this section.
Query Procedure	Stored procedure (PL/SQL) which implements the tokenization of query words. Output must be a XML document as specified in this section.

Limitations

The following features are not supported with the USER_LEXER:

• CTX_DOC.GIST and CTX_DOC.THEMES
• CTX_QUERY.HFEEDBACK
• ABOUT query operator
• CTXRULE indextype
• VGRAM indexing algorithm

USER_LEXER Attributes

The USER_LEXER has the following attributes:

Attribute	Supported Values
INDEX_PROCEDURE	Name of a stored procedure. No default provided.
INPUT_TYPE	VARCHAR2, CLOB. Default is CLOB.
QUERY_PROCEDURE	Name of a stored procedure. No default provided.

INDEX_PROCEDURE

This callback stored procedure is called by Oracle Text as needed to tokenize a document or a stop word found in the stoplist object.

Requirements

This procedure can be a PL/SQL stored procedure.

This stored procedure must be owned by user CTXSYS and the index owner must have EXECUTE privilege on it.

This stored procedure must not be replaced or dropped after the index is created. You can replace or drop this stored procedure after the index is dropped.

Parameters

Two different interfaces are supported for the user-defined lexer indexing procedure:

• VARCHAR2 Interface
• CLOB Interface

Restrictions

This procedure must not perform any of the following operations:

• rollback
• explicitly or implicitly commit the current transaction
• issue any other transaction control statement
• alter the session language or territory

The child elements of the root element tokens of the XML document returned must be in the same order as the tokens occur in the document or stop word being tokenized.

The behavior of this stored procedure must be deterministic with respect to all parameters.

INPUT_TYPE

Two different interfaces are supported for the User-defined lexer indexing procedure. One interface allows the document or stop word and the corresponding tokens encoded as XML to be passed as VARCHAR2 datatype whereas the other interface uses the CLOB datatype. This attribute indicates the interface implemented by the stored procedure specified by the INDEX_PROCEDURE attribute.

VARCHAR2 Interface

Table 2-1 describes the interface that allows the document or stop word from stoplist object to be tokenized to be passed as VARCHAR2 from Oracle Text to the stored procedure and for the tokens to be passed as VARCHAR2 as well from the stored procedure back to Oracle Text.

Your user-defined lexer indexing procedure should use this interface when all documents in the column to be indexed are smaller than or equal to 32512 bytes and the tokens can be represented by less than or equal to 32512 bytes. In this case the CLOB interface given in Table 2-2 can also be used, although the VARCHAR2 interface will generally perform faster than the CLOB interface.

This procedure must be defined with the following parameters:

Table 2-1

Parameter Position	Parameter Mode	Parameter Datatype	Description
1	IN	VARCHAR2	Document or stop word from stoplist object to be tokenized. If the document is larger than 32512 bytes then Oracle Text will report a document level indexing error.
2	IN OUT	VARCHAR2	Tokens encoded as XML. If the document contains no tokens, then either NULL must be returned or the tokens element in the XML document returned must contain no child elements. Byte length of the data must be less than or equal to 32512. To improve performance, use the NOCOPY hint when declaring this parameter. This passes the data by reference, rather than passing data by value. The XML document returned by this procedure should not include unnecessary whitespace characters (typically used to improve readability). This reduces the size of the XML document which in turn minimizes the transfer time. To improve performance, index_procedure should not validate the XML document with the corresponding XML schema at run-time. Note that this parameter is IN OUT for performance purposes. The stored procedure has no need to use the IN value.
3	IN	BOOLEAN	Is Location information needed? Oracle Text sets this parameter to TRUE when Text needs the character offset and character length of the tokens as found in the document being tokenized. Oracle Text sets this parameter to FALSE when Text is not interested in the character offset and character length of the tokens as found in the document being tokenized. This implies that the XML attributes off and len must not be used.

VARCHAR2 Interface for INDEX_PROCEDURE

CLOB Interface

Table 2-2 describes the CLOB interface that allows the document or stop word from stoplist object to be tokenized to be passed as CLOB from Oracle Text to the stored procedure and for the tokens to be passed as CLOB as well from the stored procedure back to Oracle Text.

The user-defined lexer indexing procedure should use this interface when at least one of the documents in the column to be indexed is larger than 32512 bytes or the corresponding tokens are represented by more than 32512 bytes.

Table 2-2

Parameter Position	Parameter Mode	Parameter Datatype	Description
1	IN	CLOB	Same as Table 2-1, "VARCHAR2 Interface for INDEX_PROCEDURE".
2	IN OUT	CLOB	Same as Table 2-1, "VARCHAR2 Interface for INDEX_PROCEDURE". The IN value will always be a truncated CLOB.
3	IN	BOOLEAN	Same as Table 2-1, "VARCHAR2 Interface for INDEX_PROCEDURE".

CLOB interface for INDEX_PROCEDURE

The first and second parameters are temporary CLOBS. Avoid assigning these CLOB locators to other locator variables. Assigning the formal parameter CLOB locator to another locator variable causes a new copy of the temporary CLOB to be created resulting in a performance hit.

QUERY_PROCEDURE

This callback stored procedure is called by Oracle Text as needed to tokenize words in the query. A space-delimited group of characters (excluding the query operators) in the query will be identified by Text as a word.

Requirements

This procedure can be a PL/SQL stored procedure.

This stored procedure must be owned by user CTXSYS and the index owner must have EXECUTE privilege on it.

This stored procedure must not be replaced or be dropped after the index is created. You can replace or drop this stored procedure after the index is dropped.

Restrictions

This procedure must not perform any of the following operations:

• rollback
• explicitly or implicitly commit the current transaction
• issue any other transaction control statement
• alter the session language or territory

The child elements of the root element tokens of the XML document returned must be in the same order as the tokens occur in the query word being tokenized.

The behavior of this stored procedure must be deterministic with respect to all parameters.

Parameters

Table 2-3 describes the interface for the user-defined lexer query procedure:

Table 2-3

Parameter Position	Parameter Mode	Parameter Datatype	Description
1	IN	VARCHAR2	Query word to be tokenized.
2	IN	CTX_ULEXER.WILDCARD_TAB	Character offsets of wildcard characters (% and _) in the query word. If the query word passed in by Oracle Text does not contain any wildcard characters then this index-by table will be empty. The wildcard characters in the query word must be preserved in the tokens returned in order for the wildcard query feature to work properly. The character offset is 0 (zero) based.
3	IN OUT	VARCHAR2	Tokens encoded as XML. If the query word contains no tokens then either NULL must be returned or the tokens element in the XML document returned must contain no child elements. The length of the data must be less-than or equal to 32512 bytes.

Encoding Tokens as XML

The sequence of tokens returned by your stored procedure must be represented as an XML 1.0 document. The XML document must be valid with respect to the XML Schemas given in the following sections.

• User-defined Indexing Procedure without Location XML Schema
• User-defined Indexing Procedure with Location XML Schema
• User-defined Lexer Query Procedure

Limitations

To boost performance of this feature, the XML parser in Oracle Text will not perform validation and will not be a full-featured XML compliant parser. This implies that only minimal XML features will be supported. The following XML features are not supported:

• Document Type Declaration (i.e. <!DOCTYPE [...]>) and therefore entity declarations. Only the following built-in entities can be referenced: lt, gt, amp, quot, and apos.
• CDATA sections.
• Comments.
• Processing Instructions.
• XML declaration (i.e. <?xml version="1.0" ...?>).
• Namespaces.
• Use of elements and attributes other than those defined by the corresponding XML Schema.
• Character references (e.g. &#x099F;).
• xml:space attribute.
• xml:lang attribute

User-defined Indexing Procedure without Location XML Schema

This section describes additional constraints imposed on the XML document returned by the user-defined lexer indexing procedure when the third parameter is FALSE. The XML document returned must be valid with respect to the following XML Schema:

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">

  <xsd:element name="tokens">
    <xsd:complexType>
      <xsd:sequence>
        <xsd:choice minOccurs="0" maxOccurs="unbounded"> 
          <xsd:element name="eos" type="EmptyTokenType"/>
          <xsd:element name="eop" type="EmptyTokenType"/>
          <xsd:element name="num" type="xsd:token"/> 
          <xsd:group ref="IndexCompositeGroup"/>
        </xsd:choice>
      </xsd:sequence>
    </xsd:complexType>
  </xsd:element>

  <!-- 
  Enforce constraint that compMem element must be preceeded by word element
  or compMem element for indexing 
  -->
  <xsd:group name="IndexCompositeGroup">
    <xsd:sequence>
      <xsd:element name="word" type="xsd:token"/>
      <xsd:element name="compMem" type="xsd:token" minOccurs="0"       
maxOccurs="unbounded"/>
    </xsd:sequence>
  </xsd:group>

  <!-- EmptyTokenType defines an empty element without attributes -->
  <xsd:complexType name="EmptyTokenType"/>

</xsd:schema>

Here are some of the constraints imposed by this XML Schema:

• The root element is tokens. This is mandatory. It has no attributes.
• The root element can have zero or more child elements. The child elements can be one of the following: eos, eop, num, word, and compMem. Each of these represent a specific type of token.
• The compMem element must be preceded by a word element or a compMem element.
• The eos and eop elements have no attributes and must be empty elements.
• The num, word, and compMem elements have no attributes. Oracle Text will normalize the content of these elements as follows: convert whitespace characters to space characters, collapse adjacent space characters to a single space character, remove leading and trailing spaces, perform entity reference replacement, and truncate to 64 bytes.

Table 2-4 describes the element names defined in the preceding XML Schema.

Table 2-4 Element names

Element	Description
word	This element represents a simple word token. The content of the element is the word itself. Oracle Text does the work of identifying this token as being a stop word or non-stop word and processing it appropriately.
num	This element represents an arithmetic number token. The content of the element is the arithmetic number itself. Oracle Text treats this token as a stop word if the stoplist preference has NUMBERS added as the stopclass. Otherwise this token is treated the same way as the word token. Supporting this token type is optional. Without support for this token type, adding the NUMERBS stopclass will have no effect.
eos	This element represents end-of-sentence token. Oracle Text uses this information so that it can support WITHIN SENTENCE queries. Supporting this token type is optional. Without support for this token type, queries against the SENTENCE section will not work as expected.
eop	This element represents end-of-paragraph token. Oracle Text uses this information so that it can support WITHIN PARAGRAPH queries. Supporting this token type is optional. Without support for this token type, queries against the PARAGRAPH section will not work as expected.
compMem	This element implies that the previous word token in the sequence was a composite token and that this compMem token is a constituent of that word token. Support for this token type is optional.

Example

Document: Vom Nordhauptbahnhof und aus der Innenstadt zum Messegelände.

Tokens:

<tokens>
  <word> VOM </word>
  <word> NORDHAUPTBAHNHOF </word>
  <compMem> HAUPT </compMem>
  <compMem> HAUPTBAHNHOF </compMem>
  <compMem> NORD </compMem>
  <word> UND </word>
  <word> AUS </word>
  <word> DER </word>
  <word> INNENSTADT </word>
  <word> ZUM </word>
  <word> MESSEGELÄNDE </word>
  <eos/>
</tokens>

Example

Document: Oracle9i Release 2

Tokens:

<tokens>
  <word> ORACLE9I</word>
  <word> RELEASE </word>
  <num> 2 </num>
</tokens>

Example

Document: WHERE salary<25000.00 AND job = 'F&B Manager'

Tokens:

<tokens>
  <word> WHERE </word>
  <word> salary&lt;2500.00 </word>
  <word> AND </word>
  <word> job </word>
  <word> F&amp;B </word>
  <word> Manager </word>
</tokens>

User-defined Indexing Procedure with Location XML Schema

This section describes additional constraints imposed on the XML document returned by the user-defined lexer indexing procedure when the third parameter is TRUE. The XML document returned must be valid w.r.t to the following XML schema:

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">

  <xsd:element name="tokens">
    <xsd:complexType>
      <xsd:sequence>
        <xsd:choice minOccurs="0" maxOccurs="unbounded">
          <xsd:element name="eos" type="EmptyTokenType"/>
          <xsd:element name="eop" type="EmptyTokenType"/>
          <xsd:element name="num" type="DocServiceTokenType"/>
          <xsd:group ref="DocServiceCompositeGroup"/>
        </xsd:choice>
      </xsd:sequence>
    </xsd:complexType>
  </xsd:element>

  <!-- 
  Enforce constraint that compMem element must be preceeded by word element
  or compMem element for document service
  -->
  <xsd:group name="DocServiceCompositeGroup">
    <xsd:sequence>
      <xsd:element name="word" type="DocServiceTokenType"/>
      <xsd:element name="compMem" type="DocServiceTokenType"/>
    </xsd:sequence>
  </xsd:group>

  <!-- EmptyTokenType defines an empty element without attributes -->
  <xsd:complexType name="EmptyTokenType"/>

  <!-- 
  DocServiceTokenType defines an element with content and mandatory attributes 
  -->
  <xsd:complexType name="DocServiceTokenType">
    <xsd:simpleContent>
      <xsd:extension base="xsd:token">
        <xsd:attribute name="off" type="OffsetType" use="required"/>
        <xsd:attribute name="len" type="xsd:unsignedShort" use="required"/>
      </xsd:extension>
    </xsd:simpleContent>
  </xsd:complexType>

  <xsd:simpleType name="OffsetType">
    <xsd:restriction base="xsd:unsignedInt">
      <xsd:maxInclusive value="2147483647"/>
    </xsd:restriction>
  </xsd:simpleType>

</xsd:schema>

Some of the constraints imposed by this XML Schema are as follows:

• The root element is tokens. This is mandatory. It has no attributes.
• The root element can have zero or more child elements. The child elements can be one of the following: eos, eop, num, word, and compMem. Each of these represent a specific type of token.
• The compMem element must be preceded by a word element or a compMem element.
• The eos and eop elements have no attributes and must be empty elements.
• The num, word, and compMem elements have two mandatory attributes: off and len. Oracle Text will normalize the content of these elements as follows: convert whitespace characters to space characters, collapse adjacent space characters to a single space character, remove leading and trailing spaces, perform entity reference replacement, and truncate to 64 bytes.
• The off attribute value must be an integer between 0 and 2147483647 inclusive.
• The len attribute value must be an integer between 0 and 65535 inclusive.

Table 2-4, "Element names" describes the element types defined in the preceding XML Schema.

Table 2-5, "Attributes" describes the attributes defined in the preceding XML Schema.

Table 2-5 Attributes

Attribute	Description
off	This attribute represents the character offset (same semantics as SQL function LENGTH) of the token as it appears in the document being tokenized. The offset is with respect to the character document passed to the user-defined lexer indexing procedure, not the document fetched by the datastore. The document fetched by the datastore may be pre-processed by the filter object and/or the section group object before being passed to the user-defined lexer indexing procedure. The offset of the first character in the document being tokenized is 0 (zero).
len	This attribute represents the character length (same semantics as SQL function LENGTH) of the token as it appears in the document being tokenized. The length is with respect to the character document passed to the user-defined lexer indexing procedure, not the document fetched by the datastore. The document fetched by the datastore may be pre-processed by the filter object or the section group object before being passed to the user-defined lexer indexing procedure.

Sum of off attribute value and len attribute value must be less than or equal to the total number of characters in the document being tokenized. This is to ensure that the document offset and characters being referenced are within the document boundary.

Example

Document: User-defined Lexer.

Tokens:

<tokens>
  <word off="0" len="4"> USE </word>
  <word off="5" len="7"> DEF </word>
  <word off="13" len="5"> LEX </word>
  <eos/>
</tokens>

User-defined Lexer Query Procedure

This section describes additional constraints imposed on the XML document returned by the user-defined lexer query procedure. The XML document returned must be valid with respect to the following XML Schema:

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">

  <xsd:element name="tokens">
    <xsd:complexType>
      <xsd:sequence>
        <xsd:choice minOccurs="0" maxOccurs="unbounded">
          <xsd:element name="num" type="QueryTokenType"/>
          <xsd:group ref="QueryCompositeGroup"/>
        </xsd:choice>
      </xsd:sequence>
    </xsd:complexType>
  </xsd:element>

  <!-- 
  Enforce constraint that compMem element must be preceeded by word element
  or compMem element for query
  -->
  <xsd:group name="QueryCompositeGroup">
    <xsd:sequence>
      <xsd:element name="word" type="QueryTokenType"/>
      <xsd:element name="compMem" type="QueryTokenType"/>
    </xsd:sequence>
  </xsd:group>

  <!-- 
  QueryTokenType defines an element with content and with an optional attribute
  -->
  <xsd:complexType name="QueryTokenType">
    <xsd:simpleContent>
      <xsd:extension base="xsd:token">
        <xsd:attribute name="wildcard" type="WildcardType" use="optional"/>
      </xsd:extension>
    </xsd:simpleContent>
  </xsd:complexType>

  <xsd:simpleType name="WildcardType">
    <xsd:restriction base="WildcardBaseType">
      <xsd:minLength value="1"/>
      <xsd:maxLength value="64"/>
    </xsd:restriction>     
  </xsd:simpleType>

  <xsd:simpleType name="WildcardBaseType">
    <xsd:list>
      <xsd:simpleType>
        <xsd:restriction base="xsd:unsignedShort">
          <xsd:maxInclusive value="378"/>
        </xsd:restriction>
      </xsd:simpleType>
    </xsd:list>
  </xsd:simpleType>

</xsd:schema>

Here are some of the constraints imposed by this XML Schema:

• The root element is tokens. This is mandatory. It has no attributes.
• The root element can have zero or more child elements. The child elements can be one of the following: num, word, and compMem. Each of these represent a specific type of token.
• The compMem element must be preceded by a word element or a compMem element.
• The num, word, and compMem elements have a single optional attribute: wildcard. Oracle Text will normalize the content of these elements as follows: convert whitespace characters to space characters, collapse adjacent space characters to a single space character, remove leading and trailing spaces, perform entity reference replacement, and truncate to 64 bytes.
• The wildcard attribute value is a white-space separated list of integers. The minimum number of integers is 1 and the maximum number of integers is 64. The value of the integers must be between 0 and 378 inclusive. The intriguers in the list can be in any order.

Table 2-4, "Element names" describes the element types defined in the preceding XML Schema.

Table 2-6, "Attribute for XML Schema: Query Procedure" describes the attribute defined in the preceding XML Schema.

Table 2-6 Attribute for XML Schema: Query Procedure

Attribute

Description

wildcard

Any% or _ characters in the query which are not escaped by the user are considered wildcard characters because they are replaced by other characters. These wildcard characters in the query must be preserved during tokenization in order for the wildcard query feature to work properly. This attribute represents the character offsets (same semantics as SQL function LENGTH) of wildcard characters in the content of the element. Oracle Text will adjust these offsets for any normalization performed on the content of the element. The characters pointed to by the offsets must either be% or _ characters. The offset of the first character in the content of the element is 0. If the token does not contain any wildcard characters then this attribute must not be specified.

Example

Query word: pseudo-%morph%

Tokens:

<tokens>
  <word> PSEUDO </word>
  <word wildcard="1 7"> %MORPH% </word>
</tokens>

Example

Query word: <%>
Tokens:
<tokens>
  <word wildcard="5"> &lt;%&gt; </word>
</tokens>

Wordlist Type

Use the wordlist preference to enable the query options such as stemming, fuzzy matching for your language. You can also use the wordlist preference to enable substring and prefix indexing which improves performance for wildcard queries with CONTAINS and CATSEARCH.

To create a wordlist preference, you must use BASIC_WORDLIST, which is the only type available.

BASIC_WORDLIST

Use BASIC_WORDLIST type to enable stemming and fuzzy matching or to create prefix indexes with Text indexes.

BASIC_WORDLIST has the following attributes:

Table 2-7

Attribute	Attribute Values
stemmer	Specify which language stemmer to use. You can specify one of the following: NULL (no stemming) ENGLISH (English inflectional) DERIVATIONAL (English derivational) DUTCH FRENCH GERMAN ITALIAN SPANISH AUTO (automatic language-detection for stemming)
fuzzy_match	Specify which fuzzy matching cluster to use. You can specify one of the following: GENERIC JAPANESE_VGRAM KOREAN CHINESE_VGRAM ENGLISH DUTCH FRENCH GERMAN ITALIAN SPANISH OCR AUTO (automatic language detection for stemming)
fuzzy_score	Specify a default lower limit of fuzzy score. Specify a number between 0 and 80. Text with scores below this number is not returned. Default is 60.
fuzzy_numresults	Specify the maximum number of fuzzy expansions. Use a number between 0 and 5,000. Default is 100.
substring_index	Specify TRUE for Oracle to create a substring index. A substring index improves left-truncated and double-truncated wildcard queries such as %ing or %benz%. Default is FALSE.
prefix_index	Specify TRUE to enable prefix indexing. Prefix indexing improves performance for right truncated wildcard searches such as TO%. Defaults to FALSE.
prefix_length_min	Specify the minimum length of indexed prefixes. Defaults to 1.
prefix_length_max	Specify the maximum length of indexed prefixes. Defaults to 64.
wlidcard_maxterms	Specify the maximum number of terms in a wildcard expansion. Use a number between 1 and 15,000. Default is 5,000.

stemmer

Specify the stemmer used for word stemming in Text queries. When you do not specify a value for stemmer, the default is ENGLISH.

Specify AUTO for the system to automatically set the stemming language according to the language setting of the session. When there is no stemmer for a language, the default is NULL. With the NULL stemmer, the stem operator is ignored in queries.

fuzzy_match

Specify which fuzzy matching routines are used for the column. Fuzzy matching is currently supported for English, Japanese, and, to a lesser extent, the Western European languages.

The default for fuzzy_match is GENERIC.

Specify AUTO for the system to automatically set the fuzzy matching language according to language setting of the session.

fuzzy_score

Specify a default lower limit of fuzzy score. Specify a number between 0 and 80. Text with scores below this below this number are not returned. The default is 60.

Fuzzy score is a measure of how close the expanded word is to the query word. The higher the score the better the match. Use this parameter to limit fuzzy expansions to the best matches.

fuzzy_numresults

Specify the maximum number of fuzzy expansions. Use a number between 0 and 5000. The default is 100.

Setting a fuzzy expansion limits the expansion to a specified number of the best matching words.

substring_index

Specify TRUE for Oracle to create a substring index. A substring index improves performance for left-truncated or double-truncated wildcard queries such as %ing or %benz%. The default is false.

Substring indexing has the following impact on indexing and disk resources:

• Index creation and DML processing is up to 4 times slower
• The size of the substring index created is approximately the size of the $X index on the word table.
• Index creation with substring_index enabled requires more rollback segments during index flushes than with substring index off. Oracle recommends that you do either of the following when creating a substring index:
  • make available double the usual rollback or
  • decrease the index memory to reduce the size of the index flushes to disk

prefix_index

Specify yes to enable prefix indexing. Prefix indexing improves performance for right truncated wildcard searches such as TO%. Defaults to NO.

Prefix indexing chops up tokens into multiple prefixes to store in the $I table.For example, words TOKEN and TOY are normally indexed like this in the $I table:

Token	Type	Information
TOKEN	0	DOCID 1 POS 1
TOY	0	DOCID 1 POS 3

With prefix indexing, Oracle indexes the prefix substrings of these tokens as follows with a new token type of 6:

Token	Type	Information
TOKEN	0	DOCID 1 POS 1
TOY	0	DOCID 1 POS 3
T	6	DOCID 1 POS 1 POS 3
TO	6	DOCID 1 POS 1 POS 3
TOK	6	DOCID 1 POS 1
TOKE	6	DOCID 1 POS 1
TOKEN	6	DOCID 1 POS 1
TOY	6	DOCID 1 POS 3

Wildcard searches such as TO% are now faster because Oracle does no expansion of terms and merging of result sets. To obtain the result, Oracle need only examine the (TO,6) row.

prefix_length_min

Specify the minimum length of indexed prefixes. Defaults to 1.

For example, setting prefix_length_min to 3 and prefix_length_max to 5 indexes all prefixes between 3 and 5 characters long.

prefix_length_max

Specify the maximum length of indexed prefixes. Defaults to 64.

For example, setting prefix_length_min to 3 and prefix_length_max to 5 indexes all prefixes between 3 and 5 characters long.

wildcard_maxterms

Specify the maximum number of terms in a wildcard (%) expansion. Use this parameter to keep wildcard query performance within an acceptable limit. Oracle returns an error when the wildcard query expansion exceeds this number.

BASIC_WORDLIST Example

Enabling Fuzzy Matching and Stemming

The following example enables stemming and fuzzy matching for English. The preference STEM_FUZZY_PREF sets the number of expansions to the maximum allowed. This preference also instructs the system to create a substring index to improve the performance of double-truncated searches.

begin 
  ctx_ddl.create_preference('STEM_FUZZY_PREF', 'BASIC_WORDLIST'); 
  ctx_ddl.set_attribute('STEM_FUZZY_PREF','FUZZY_MATCH','ENGLISH');
  ctx_ddl.set_attribute('STEM_FUZZY_PREF','FUZZY_SCORE','0');
  ctx_ddl.set_attribute('STEM_FUZZY_PREF','FUZZY_NUMRESULTS','5000');
  ctx_ddl.set_attribute('STEM_FUZZY_PREF','SUBSTRING_INDEX','TRUE');
  ctx_ddl.set_attribute('STEM_FUZZY_PREF','STEMMER','ENGLISH');
end; 

To create the index in SQL, issue the following statement:

create index fuzzy_stem_subst_idx on mytable ( docs ) 
  indextype is ctxsys.context parameters ('Wordlist STEM_FUZZY_PREF');

Enabling Sub-string and Prefix Indexing

The following example sets the wordlist preference for prefix and sub-string indexing. For prefix indexing, it specifies that Oracle create token prefixes between 3 and 4 characters long:

begin 


ctx_ddl.create_preference('mywordlist', 'BASIC_WORDLIST'); 
ctx_ddl.set_attribute('mywordlist','PREFIX_INDEX','TRUE');
ctx_ddl.set_attribute('mywordlist','PREFIX_MIN_LENGTH',3);
ctx_ddl.set_attribute('mywordlist','PREFIX_MAX_LENGTH', 4);
ctx_ddl.set_attribute('mywordlist','SUBSTRING_INDEX', 'YES');

end

Setting Wildcard Expansion Limit

Use the wildcard_maxterms attribute to set the maximum allowed terms in a wildcard expansion.

--- create a sample table
drop table quick ;
create table quick 
  ( 
    quick_id number primary key, 
    text      varchar(80) 
  ); 

--- insert a row with 10 expansions for 'tire%'
insert into quick ( quick_id, text ) 
  values ( 1, 'tire tirea tireb tirec tired tiree tiref tireg tireh tirei 
tirej') ;
commit;

--- create an index using wildcard_maxterms=100
begin 
    Ctx_Ddl.Create_Preference('wildcard_pref', 'BASIC_WORDLIST'); 
    ctx_ddl.set_attribute('wildcard_pref', 'wildcard_maxterms', 100) ;
end; 
/
create index wildcard_idx on quick(text)
    indextype is ctxsys.context 
    parameters ('Wordlist wildcard_pref') ;

--- query on 'tire%' - should work fine
select quick_id from quick
  where contains ( text, 'tire%' ) > 0;

--- now re-create the index with wildcard_maxterms=5

drop index wildcard_idx ;

begin 
    Ctx_Ddl.Drop_Preference('wildcard_pref'); 
    Ctx_Ddl.Create_Preference('wildcard_pref', 'BASIC_WORDLIST'); 
    ctx_ddl.set_attribute('wildcard_pref', 'wildcard_maxterms', 5) ;
end; 
/

create index wildcard_idx on quick(text)
    indextype is ctxsys.context 
    parameters ('Wordlist wildcard_pref') ;

--- query on 'tire%' gives "wildcard query expansion resulted in too many terms"
select quick_id from quick
  where contains ( text, 'tire%' ) > 0;

Storage Types

Use the storage preference to specify tablespace and creation parameters for tables associated with a Text index. The system provides a single storage type called BASIC_STORAGE:

type	Description
BASIC_STORAGE	Indexing type used to specify the tablespace and creation parameters for the database tables and indexes that constitute a Text index.

BASIC_STORAGE

The BASIC_STORAGE type specifies the tablespace and creation parameters for the database tables and indexes that constitute a Text index.

The clause you specify is added to the internal CREATE TABLE (CREATE INDEX for the i_index _clause) statement at index creation. You can specify most allowable clauses, such as storage, LOB storage, or partitioning. However, you cannot specify an index organized table clause.

BASIC_STORAGE has the following attributes:

Attribute	Attribute Value
i_table_clause	Parameter clause for dr$indexname$I table creation. Specify storage and tablespace clauses to add to the end of the internal CREATE TABLE statement. The I table is the index data table.
k_table_clause	Parameter clause for dr$indexname$K table creation. Specify storage and tablespace clauses to add to the end of the internal CREATE TABLE statement. The K table is the keymap table.
r_table_clause	Parameter clause for dr$indexname$R table creation. Specify storage and tablespace clauses to add to the end of the internal CREATE TABLE statement. The R table is the rowid table. The default clause is: 'LOB(DATA) STORE AS (CACHE)'
n_table_clause	Parameter clause for dr$indexname$N table creation. Specify storage and tablespace clauses to add to the end of the internal CREATE TABLE statement. The N table is the negative list table.
i_index_clause	Parameter clause for dr$indexname$X index creation. Specify storage and tablespace clauses to add to the end of the internal CREATE INDEX statement. The default clause is: 'COMPRESS 2' which instructs Oracle to compress this index table. If you choose to override the default, Oracle recommends including COMPRESS 2 in your parameter clause to compress this table, since such compression saves disk space and helps query performance.
p_table_clause	Parameter clause for the substring index if you have enabled SUBSTRING_INDEX in the BASIC_WORDLIST. Specify storage and tablespace clauses to add to the end of the internal CREATE INDEX statement. The P table is an index-organized table so the storage clause you specify must be appropriate to this type of table.

Storage Default Behavior

By default, BASIC_STORAGE attributes are not set. In such cases, the Text index tables are created in the index owner's default tablespace. Consider the following statement, issued by user IUSER, with no BASIC_STORAGE attributes set:

create index IOWNER.idx on TOWNER.tab(b) indextype is ctxsys.context;

In this example, the text index is created in IOWNER's default tablespace.

Storage Example

The following examples specify that the index tables are to be created in the foo tablespace with an initial extent of 1K:

begin
ctx_ddl.create_preference('mystore', 'BASIC_STORAGE');
ctx_ddl.set_attribute('mystore', 'I_TABLE_CLAUSE',
                        'tablespace foo storage (initial 1K)'); 
ctx_ddl.set_attribute('mystore', 'K_TABLE_CLAUSE',
                        'tablespace foo storage (initial 1K)'); 
ctx_ddl.set_attribute('mystore', 'R_TABLE_CLAUSE',
                        'tablespace foo storage (initial 1K)'); 
ctx_ddl.set_attribute('mystore', 'N_TABLE_CLAUSE',
                        'tablespace foo storage (initial 1K)'); 
ctx_ddl.set_attribute('mystore', 'I_INDEX_CLAUSE',
                        'tablespace foo storage (initial 1K)'); 
ctx_ddl.set_attribute('mystore', 'P_TABLE_CLAUSE',
                        'tablespace foo storage (initial 1K)'); 
end;

Section Group Types

In order to issue WITHIN queries on document sections, you must create a section group before you define your sections. You specify your section group in the parameter clause of CREATE INDEX.

To create a section group, you can specify one of the following group types with the CTX_DDL.CREATE_SECTION_GROUP procedure:

Section Group Preference	Description
NULL_SECTION_GROUP	Use this group type when you define no sections or when you define only SENTENCE or PARAGRAPH sections. This is the default.
BASIC_SECTION_GROUP	Use this group type for defining sections where the start and end tags are of the form <A> and </A>. Note: This group type dopes not support input such as unbalanced parentheses, comments tags, and attributes. Use HTML_SECTION_GROUP for this type of input.
HTML_SECTION_GROUP	Use this group type for indexing HTML documents and for defining sections in HTML documents.
XML_SECTION_GROUP	Use this group type for indexing XML documents and for defining sections in XML documents.
AUTO_SECTION_GROUP	Use this group type to automatically create a zone section for each start-tag/end-tag pair in an XML document. The section names derived from XML tags are case sensitive as in XML. Attribute sections are created automatically for XML tags that have attributes. Attribute sections are named in the form attribute@tag. Stop sections, empty tags, processing instructions, and comments are not indexed. The following limitations apply to automatic section groups: You cannot add zone, field, or special sections to an automatic section group. Automatic sectioning does not index XML document types (root elements.) However, you can define stop sections with document type. The length of the indexed tags, including prefix and namespace, cannot exceed 64 characters. Tags longer than this are not indexed.
PATH_SECTION_GROUP	Use this group type to index XML documents. Behaves like the AUTO_SECTION_GROUP. The difference is that with this section group you can do path searching with the INPATH and HASPATH operators. Queries are also case-sensitive for tag and attribute names. Stop sections are not allowed.
NEWS_SECTION_GROUP	Use this group for defining sections in newsgroup formatted documents according to RFC 1036.

Section Group Examples

Creating Section Groups in HTML Documents

The following statement creates a section group called htmgroup with the HTML group type.

begin
ctx_ddl_create_section_group('htmgroup', 'HTML_SECTION_GROUP');
end;

You can optionally add sections to this group using the CTX_DDL.ADD_SECTION procedure. To index your documents, you can issue a statement such as:

create index myindex on docs(htmlfile) indextype is ctxsys.context 
parameters('filter ctxsys.null_filter section group htmgroup');

Creating Sections Groups in XML Documents

The following statement creates a section group called xmlgroup with the XML_SECTION_GROUP group type.

begin
ctx_ddl_create_section_group('xmlgroup', 'XML_SECTION_GROUP');
end;

You can optionally add sections to this group using the CTX_DDL.ADD_SECTION procedure. To index your documents, you can issue a statement such as:

create index myindex on docs(htmlfile) indextype is ctxsys.context 
parameters('filter ctxsys.null_filter section group xmlgroup');

Automatic Sectioning in XML Documents

The following statement creates a section group called auto with the AUTO_SECTION_GROUP group type. This section group automatically creates sections from tags in XML documents.

begin


ctx_ddl_create_section_group('auto', 'AUTO_SECTION_GROUP');

end; CREATE INDEX myindex on docs(htmlfile) INDEXTYPE IS ctxsys.context PARAMETERS('filter ctxsys.null_filter section group auto');

Classifier Types

This section describes the classifier type used to create a preference for CTX_CLS.TRAIN.

RULE_CLASSIFIER

Use the RULE_CLASSIFIER type for creating preferences for the rule generating procedure, CTX_CLS.TRAIN.

This type has the following attributes:

Attribute Name	Data Type	Default	Min Value	Max Value	Description
THRESHOLD	I	50	1	99	Threshold (in percentage) from rule generation. One rule is output only when its confidence level is larger than threshold.
MAX_TERMS	I	100	20	2000	For each class, a list of relevant terms is selected to form rules. This attribute specifies the maximum number of terms that can be selected for each class.
MEMORY_SIZE	I	500	10	4000	Typical memory usage for training in MB. Larger values improve performance.
NT_THRESHOLD	F	0.001	0	0.90	A threshold for term selection. There are two thresholds guiding two steps in selecting relevant terms. This threshold controls the behavior of the first step. At this step, terms are selected as candidate terms for the further consideration in the second step. The term is chosen when the ratio of the occurrence frequency over the number of documents in the training set is larger than this threshold.
TERM_THRESHOLD	I	10	0	100	Threshold as a percentage for term selection. This threshold controls the second step term selection. Each candidate term has a numerical quantity calculated to imply its correlation with a given class. The candidate term will be selected for this class only when the ratio of its quantity value over the maximum value for all candidate terms in the class is larger than this threshold.

Stoplists

Stoplists identify the words in your language that are not to be indexed. In English, you can also identify stopthemes that are not to be indexed. By default, the system indexes text using the system-supplied stoplist that corresponds to your database language.

Oracle Text provides default stoplists for most languages including English, French, German, Spanish, Dutch, and Danish. These default stoplists contain only stopwords.

Multi-Language Stoplists

You can create multi-language stoplists to hold language-specific stopwords. A multi-language stoplist is useful when you use the MULTI_LEXER to index a table that contains documents in different languages, such as English, German, and Japanese.

To create a multi-language stoplist, use the CTX_DLL.CREATE_STOPLIST procedure and specify a stoplist type of MULTI_STOPLIST. You add language specific stopwords with CTX_DDL.ADD_STOPWORD.

At indexing time, the language column of each document is examined, and only the stopwords for that language are eliminated. At query time, the session language setting determines the active stopwords, like it determines the active lexer when using the multi-lexer.

Creating Stoplists

You can create your own stoplists using the CTX_DLL.CREATE_STOPLIST procedure. With this procedure you can create a BASIC_STOPLIST for single language stoplist, or you can create a MULTI_STOPLIST for a multi-language stoplist.

When you create your own stoplist, you must specify it in the parameter clause of CREATE INDEX.

Modifying the Default Stoplist

The default stoplist is always named CTXSYS.DEFAULT_STOPLIST. You can use the following procedures to modify this stoplist:

• CTX_DDL.ADD_STOPWORD
• CTX_DDL.REMOVE_STOPWORD
• CTX_DDL.ADD_STOPTHEME
• CTX_DDL.ADD_STOPCLASS

When you modify CTXSYS.DEFAULT_STOPLIST with the CTX_DDL package, you must re-create your index for the changes to take effect.

Dynamic Addition of Stopwords

You can add stopwords dynamically to a default or custom stoplist with ALTER INDEX. When you add a stopword dynamically, you need not re-index, because the word immediately becomes a stopword and is removed from the index.

System-Defined Preferences

When you install Oracle Text, some indexing preferences are created. You can use these preferences in the parameter clause of CREATE INDEX or define your own.

The default index parameters are mapped to some of the system-defined preferences described in this section.

System-defined preferences are divided into the following categories:

• Data Storage
• Filter
• Lexer
• Section Group
• Stoplist
• Storage
• Wordlist

Data Storage

CTXSYS.DEFAULT_DATASTORE

This preference uses the DIRECT_DATASTORE type. You can use this preference to create indexes for text columns in which the text is stored directly in the column.

CTXSYS.FILE_DATASTORE

This preference uses the FILE_DATASTORE type.

CTXSYS.URL_DATASTORE

This preference uses the URL_DATASTORE type.

Filter

CTXSYS.NULL_FILTER

This preference uses the NULL_FILTER type.

CTXSYS.INSO_FILTER

This preference uses the INSO_FILTER type.

Lexer

CTXSYS.DEFAULT_LEXER

The default lexer depends on the language used at install time. The following sections describe the default settings for CTXSYS.DEFAULT_LEXER for each language.

American and English Language Settings

If your language is English, this preference uses the BASIC_LEXER with the index_themes attribute disabled.

Danish Language Settings

If your language is Danish, this preference uses the BASIC_LEXER with the following option enabled:

• alternate spelling (alternate_spelling attribute set to DANISH)

Dutch Language Settings

If your language is Dutch, this preference uses the BASIC_LEXER with the following options enabled:

• composite indexing (composite attribute set to DUTCH)

German and German DIN Language Settings

If your language is German, this preference uses the BASIC_LEXER with the following options enabled:

• case-sensitive indexing (mixed_case attribute enabled)
• composite indexing (composite attribute set to GERMAN)
• alternate spelling (alternate_spelling attribute set to GERMAN)

Finnish, Norwegian, and Swedish Language Settings

If your language is Finnish, Norwegian, or Swedish, this preference uses the BASIC_LEXER with the following option enabled:

• alternate spelling (alternate_spelling attribute set to SWEDISH)

Japanese Language Settings

If you language is Japanese, this preference uses the JAPANESE_VGRAM_LEXER.

Korean Language Settings

If your language is Korean, this preference uses the KOREAN_MORPH_LEXER. All attributes for the KOREAN_MORPH_LEXER are enabled.

Chinese Language Settings

If your language is Simplified or Traditional Chinese, this preference uses the CHINESE_VGRAM_LEXER.

Other Languages

For all other languages not listed in this section, this preference uses the BASIC_LEXER with no attributes set.

CTXSYS.BASIC_LEXER

This preference uses the BASIC_LEXER.

Section Group

CTXSYS.NULL_SECTION_GROUP

This preference uses the NULL_SECTION_GROUP type.

CTXSYS.HTML_SECTION_GROUP

This preference uses the HTML_SECTION_GROUP type.

CTXSYS.AUTO_SECTION_GROUP

This preference uses the AUTO_SECTION_GROUP type.

CTXSYS.PATH_SECTION_GROUP

This preference uses the PATH_SECTION_GROUP type.

Stoplist

CTXSYS.DEFAULT_STOPLIST

This stoplist preference defaults to the stoplist of your database language.

CTXSYS.EMPTY_STOPLIST

This stoplist has no words.

Storage

CTXSYS.DEFAULT_STORAGE

This storage preference uses the BASIC_STORAGE type.

Wordlist

CTXSYS.DEFAULT_WORDLIST

This preference uses the language stemmer for your database language. If your language is not listed in Table 2-7, this preference defaults to the NULL stemmer and the GENERIC fuzzy matching attribute.

System Parameters

This section describes the Oracle Text system parameters. They fall into the following categories:

• General System Parameters
• Default Index Parameters

General System Parameters

When you install Oracle Text, in addition to the system-defined preferences, the following system parameters are set:

System Parameter	Description
MAX_INDEX_MEMORY	This is the maximum indexing memory that can be specified in the parameter clause of CREATE INDEX and ALTER INDEX.
DEFAULT_INDEX_MEMORY	This is the default indexing memory used with CREATE INDEX and ALTER INDEX.
LOG_DIRECTORY	This is the directory for CTX_OUTPUT log files.
CTX_DOC_KEY_TYPE	This is the default input key type, either ROWID or PRIMARY_KEY, for the CTX_DOC procedures. Set to ROWID at install time. See also: CTX_DOC. SET_KEY_TYPE.

You can view system defaults by querying the CTX_PARAMETERS view. You can change defaults using the CTX_ADM.SET_PARAMETER procedure.

Default Index Parameters

This section describes the index parameters you can use when you create context and ctxcat indexes.

CONTEXT Index Parameters

The following default parameters are used when you do not specify preferences in the parameter clause of CREATE INDEX when you create a context index. Each default parameter names a system-defined preference to use for data storage, filtering, lexing, and so on.

System Parameter	Used When	Default Value
DEFAULT_DATASTORE	No datastore preference specified in parameter clause of CREATE INDEX.	CTXSYS.DEFAULT_DATASTORE
DEFAULT_FILTER_FILE	No filter preference specified in parameter clause of CREATE INDEX, and either of the following conditions is true: Your files are stored in external files (BFILES) or You specify a datastore preference that uses FILE_DATASTORE	CTXSYS.INSO_FILTER
DEFAULT_FILTER_BINARY	No filter preference specified in parameter clause of CREATE INDEX, and Oracle detects that the text column datatype is RAW, LONG RAW, or BLOB.	CTXSYS.INSO_FILTER
DEFAULT_FILTER_TEXT	No filter preference specified in parameter clause of CREATE INDEX, and Oracle detects that the text column datatype is either LONG, VARCHAR2, VARCHAR, CHAR, or CLOB.	CTXSYS.NULL_FILTER
DEFAULT_SECTION_HTML	No section group specified in parameter clause of CREATE INDEX, and when either of the following conditions is true: Your datastore preference uses URL_DATASTORE or Your filter preference uses INSO_FILTER.	CTXSYS.HTML_SECTION_GROUP
DEFAULT_SECTION_TEXT	No section group specified in parameter clause of CREATE INDEX, and when you do not use either URL_DATASTORE or INSO_FILTER.	CTXSYS.NULL_SECTION_GROUP
DEFAULT_STORAGE	No storage preference specified in parameter clause of CREATE INDEX.	CTXSYS.DEFAULT_STORAGE
DEFAULT_LEXER	No lexer preference specified in parameter clause of CREATE INDEX.	CTXSYS.DEFAULT_LEXER
DEFAULT_STOPLIST	No stoplist specified in parameter clause of CREATE INDEX.	CTXSYS.DEFAULT_STOPLIST
DEFAULT_WORDLIST	No wordlist preference specified in parameter clause of CREATE INDEX.	CTXSYS.DEFAULT_WORDLIST

CTXCAT Index Parameters

The following default parameters are used when you create a CTXCAT index with CREATE INDEX and do not specify any parameters in the parameter string. The CTXCAT index supports only the index set, lexer, storage, stoplist, and wordlist parameters. Each default parameter names a system-defined preference.

System Parameter	Used When	Default Value
DEFAULT_CTXCAT_INDEX_SET	No index set specified in parameter clause of CREATE INDEX.
DEFAULT_CTXCAT_STORAGE	No storage preference specified in parameter clause of CREATE INDEX.	CTXSYS.DEFAULT_STORAGE
DEFAULT_CTXCAT_LEXER	No lexer preference specified in parameter clause of CREATE INDEX.	CTXSYS.DEFAULT_LEXER
DEFAULT_CTXCAT_STOPLIST	No stoplist specified in parameter clause of CREATE INDEX.	CTXSYS.DEFAULT_STOPLIST
DEFAULT_CTXCAT_WORDLIST	No wordlist preference specified in parameter clause of CREATE INDEX. Note that while you can specify a wordlist preference for CTXCAT indexes, most of the attributes do not apply, since the catsearch query language does not support wildcarding, fuzzy, and stemming. The only attribute that is useful is PREFIX_INDEX for Japanese data.	CTXSYS.DEFAULT_WORDLIST

CTXRULE Index Parameters

The following default parameters are used when you create a CTXRULE index with CREATE INDEX and do not specify any parameters in the parameter string. The CTXRULE index supports only the lexer, storage, stoplist, and wordlist parameters. Each default parameter names a system-defined preference.

System Parameter	Used When	Default Value
DEFAULT_CTXRULE_LEXER	No lexer preference specified in parameter clause of CREATE INDEX.	CTXSYS.DEFAULT_LEXER
DEFAULT_CTXRULE_STORAGE	No storage preference specified in parameter clause of CREATE INDEX.	CTXSYS.DEFAULT_STORAGE
DEFAULT_CTXRULE_STOPLIST	No stoplist specified in parameter clause of CREATE INDEX.	CTXSYS.DEFAULT_STOPLIST
DEFAULT_CTXRULE_WORDLIST	No wordlist preference specified in parameter clause of CREATE INDEX.	CTXSYS.DEFAULT_WORDLIST

Viewing Default Values

You can view system defaults by querying the CTX_PARAMETERS view. For example, to see all parameters and values, you can issue:

SQL> SELECT par_name, par_value from ctx_parameters;

Changing Default Values

You can change a default value using the CTX_ADM.SET_PARAMETER procedure to name another custom or system-defined preference to use as default.