Tasks That an OLAP API Application Performs

An application that uses the OLAP API typically performs the following tasks:

1. Connect to the data store
2. Discover the available metadata
3. Select and calculate data through queries
4. Retrieve query results

The rest of this topic briefly describes these tasks, and the rest of this guide provides detailed information.

Task 1: Connect to the Data Store

An application connects to the data store by identifying some information about the target Oracle database and specifying this information in a JDBC connection method.

For more information about connecting, see Chapter 3, "Connecting to a Data Store".

Task 2: Discover the Available Metadata

Having established a connection, the application creates an MdmMetadataProvider. This object gives access to all the metadata objects in the data store.

To discover the available metadata, an application uses the getRootSchema method on the MdmMetdataProvider to obtain the top-level measure folder for all of its metadata objects. The application then gets the dimensions, measures, and subfolders that are under the root. Once the application has all the dimensions and measures, it can interrogate them to get their attributes, hierarchies, levels, and other characteristics.

Having determined the metadata objects that it has to work with, the application can present relevant lists of objects to the user for data selection and manipulation.

For a description of the metadata objects, see Chapter 2, "Understanding OLAP API Metadata". For information about how an application can discover the available metadata, see Chapter 4, "Discovering the Available Metadata".

Task 3: Select and Calculate Data Through Queries

The heart of any OLAP application lies in the construction of queries against the data store. The application user interface provides ways for the user to select data and specify what should be done with it. Then, the data manipulation code translates these instructions into queries against the data store. The queries can be as simple as a selection of dimension elements, or they can be complex, including several aggregations and calculations on measure values.

The OLAP API object that specifies a query is a Source. Therefore, a significant portion of any OLAP API application is devoted to dealing with Source objects.

You can manipulate Source objects directly, using methods such as select, remove, and appendValues to create selections. In addition, you can use methods such as plus, div, and total to calculate values. Source and its subclasses, NumberSource, StringSource, and BooleanSource, have a rich assortment of methods for manipulating data. The most powerful method in Source is join, which gives you the ability to combine Source objects in almost any way imaginable.

If you are implementing a simple user interface, you might use only the methods on the Source classes to select and manipulate the data that users specify in the interface. However, if you want to offer your users multistep selection procedures and the ability to modify queries or undo individual steps in their selections, you should use Template classes as described in the topic "Developing an OLAP API Application" . Within the code for each Template, you use the methods on the Source classes, but the Template classes themselves allow you to modify and refine even the most complex query. In addition, you can minimize your work by writing general-purpose Template classes and reusing them in various parts of your application.

For information about working with Source objects, see Chapter 5, "Introduction to Querying". For information about working with Template objects, see Chapter 10, "Creating Dynamic Queries".

Task 4: Retrieve Query Results

When users of an OLAP application are selecting, calculating, combining, and generally manipulating data, they also want to see the results of their work. This means that the application must retrieve the result sets of queries from the data store and display the data in multidimensional form. To retrieve a result set for a query through the OLAP API, the application creates a Cursor based on the Source that specifies the query.

Because the OLAP API was designed to deal with a multidimensional view of data, a Source can have a multidimensional result set. For example, a Source can represent an MdmMeasure that is structured by three MdmDimension objects. The Cursor for this Source has a structure that mirrors the Source itself; that is, the Cursor organization is based on the same three MdmDimension objects.

To retrieve all the items of data through a Cursor, the application can loop through the multidimensional Cursor structure. This design is well adapted to the requirements of standard user interface objects for painting the computer screen. It is especially well adapted to the display of data in multidimensional format.

For more information about using Cursor objects to retrieve data, see Chapter 8, "Understanding Cursor Classes and Concepts".