Overview of the Procedure for Discovering Metadata

The OLAP API provides access to a collection of Oracle data for which a database administrator has created OLAP metadata using the OLAP Metadata APIs. This collection of data is the data store for the application.

Potentially, the data store includes all of the measure folders that were created by the database administrator using the OLAP Metadata APIs. However, the scope of the data store that is visible when a given application is running depends on the database privileges that apply to the user ID through which the connection was made. A user sees all of the measure folders (as MdmSchema objects) that the database administrator created, but the user sees the measures and dimensions that are contained in those measure folders only if he or she has access rights to the relational tables on which the measures and dimensions are based.

MDM Metadata

When the database administrator created the metadata, the OLAP Metadata APIs created measures, dimensions, and other OLAP metadata objects. In the OLAP API, these objects are accessed as multidimensional metadata (MDM) objects, as described in Chapter 2, "Understanding OLAP API Metadata". The mapping between the OLAP metadata objects and the MDM objects is automatically performed by Oracle OLAP.

Purpose of Discovering the Metadata

The metadata objects in the data store help your application to make sense of the data. They provide a way for you to find out what data is available, how it is structured, and what its characteristics are.

Therefore, after connecting, your first step is to find out what metadata is available. Armed with this knowledge, you can present choices to the end user about what data should be selected or calculated and how it should be displayed.

Steps in Discovering the Metadata

Before investigating the metadata, your application must make a connection to Oracle OLAP, as described in Chapter 3, "Connecting to a Data Store". Then, your application performs the following steps:

1. Create an MdmMetadataProvider
2. Get the root MdmSchema from the MdmMetadataProvider
3. Get the contents of the root MdmSchema, which include MdmMeasure, MdmDimension, MdmMeasureDimension, and MdmSchema objects. In addition, get the contents of any subschemas.
4. Get the characteristics of each MdmMeasure and MdmDimension. For example, for each MdmMeasure get its MdmDimension objects, and for each MdmDimension find out whether it is a union MdmHierarchy, a level MdmHierarchy, an MdmLevel, or an MdmListDimension.

The next four topics in this chapter describe these steps in detail.

Discovering Metadata and Making Queries

After you discover the metadata, you typically go on to create queries for selecting, calculating, and otherwise manipulating the data. In order to work with data in these ways, you must get the Source objects that Oracle OLAP has created to represent the data for querying. These Source objects are referred to as primary Source objects.

This chapter focuses on the initial step of discovering the available metadata, but it also briefly mentions the step of getting a primary Source from a metadata object. Subsequent chapters of this guide explain how you work with primary Source objects and create queries based on them.