OLAP Metadata Objects

Using the OLAP Metadata APIs, a database administrator adds OLAP metadata to a data warehouse. The end result is the creation of one or more measure folders that contain one or more measures. The measures have dimensions, and the dimensions have hierarchies, levels, and attributes. Each of these OLAP metadata objects maps directly to an MDM object in the OLAP API.

For detailed information about OLAP metadata and about using the OLAP Metadata APIs, see the Oracle9i OLAP User's Guide.

Note that the OLAP metadata includes a cube object, which does not map directly to any MDM object. Database administrators reference cubes in the OLAP Metadata APIs when they specify the dimensions of each measure. Once the dimensions are specified, they are firmly associated with their measures in the metadata, so this type of cube object is not needed in the MDM model.

The rest of this topic briefly describes the OLAP metadata objects that map directly to MDM objects in the OLAP API.

Dimensions in the OLAP Metadata

The he following are some of the characteristics that a database administrator can specify for dimensions:

• General characteristics, such as the name of the dimension and the schema from which its data is drawn.
• Levels, which record the levels of the dimension. The database administrator typically specifies one or more levels for each OLAP dimension.
• Hierarchies, which specify the parent-child relationships between the levels. The database administrator typically specifies at least one hierarchy for each OLAP dimension. If there is only one level for the dimension, then no hierarchy is specified and the dimension is a simple, non-hierarchical list.
• Attributes, which record characteristics of the level elements for the dimension. For example, an attribute might record the gender of each customer in the customers dimension.

Typically, a database administrator specifies one or more columns in a database table to serve as the basis for each OLAP level, hierarchy, and attribute.

A database administrator creates cubes after creating dimensions. A cube is a set of dimensions that provide organizational structure for measures.

Measures in the OLAP Metadata

The OLAP Metadata APIs give a database administrator the ability to specify that a given measure belongs to a given cube. Because a cube is a set of dimensions that provide organizational structure for measures, specifying that a given measure belongs to a given cube specifies the dimensions of that measure. This is essential information for the OLAP API, where the dimensionality of a measure is one of its most important features.

To identify the data for a measure, the database administrator typically specifies a column in a fact table where the measure's data resides. As an alternative, the database administrator can specify a calculation or transformation that produces the data.

Measure Folders in the OLAP Metadata

Once a database administrator has created measures (first creating dimensions and cubes), the next step is to create one or more groups of measures called measure folders. Typically, the measures in a given folder are related by subject matter. That is, they all pertain to the same business area. For example, there might be three separate folders for financials, sales, and human resources.

The measures in a given measure folder can belong to different cubes, and they can be from more than one schema.

The database administrator must create at least one measure folder because the scope of the data that an OLAP API application can access is defined in terms of measure folders. That is, an OLAP API MdmMetadataProvider gives access only to the measures that are contained in measure folders. Of course, each measure's dimensions are included, along with its hierarchies, levels, and attributes.

In this context, it is important to understand that measure folders can be nested. This means that a given measure folder can have subfolders that have their own measures, and even their own subfolders. Thus, a database administrator can arrange measures in a hierarchy of folders, and an OLAP API MdmMetadataProvider can give access to all of the measure folders and their subfolders.