How Does the OLAP API Represent Queries?

What objects represent queries?

In the OLAP API, queries are represented by two objects:

• The specification for a query is represented by a Source object. Source objects merely describe the data. They are not actual result sets.

• The result set of a query is a Cursor object. Cursor objects are the objects that you use to actually retrieve data from the database.

Only some of the query specifications represented by Source objects represent queries that the OLAP service can retrieve from a database and process. The kinds of Source objects for which you can define a Cursor and the use of Cursor objects are described more completely in Chapter 9.

Source objects are immutable. You cannot change a Source object once it has been created. When you want to present a Source object as changeable to your users (for example, to support what-if analysis), use a Source object defined by a Template object. Template objects themselves have state and can be modified at any time. For more information on using Template objects, see Chapter 11.

What are the subclasses of the Source class?

As outlined in the following table, the Source class has different subclasses for different data types. Each of the subclasses defines methods that are type-specific versions of various Source methods and methods that perform type-specific operations.

Class	Java Type of Element Values	OLAP API Data Type
BooleanSource	boolean values	Boolean
DateSource	Java Date objects	Date
NumberSource	double, float, int, or short values, or some combination of these numerical values	Double, Float, Integer, Short, or Number.
StringSource	Java String objects	String

For more information on these subclasses, see the online reference documentation for the OLAP API. For more information on OLAP API data type, see "Getting and Working with Fundamental Source Objects".

What kinds of Source objects are there?

The OLAP API has the following kinds of Source objects:

• Primary Source objects which are Source objects that correspond to metadata objects. Primary Source objects have a structure that is similar to the metadata objects from which they are created.

• Derived Source objects which are new Source objects that are created by manipulating existing Source objects.

• Fundamental Source objects which are Source objects that represent data types and functions that are intrinsic to the OLAP API.

• Constant, list, and range Source objects which are simple nondimensional Source objects that you can use as operands when making selections and calculations.

Since a Source is an object, you must obtain an object reference to it in order to use it. The way you obtain an object reference to a Source varies by the kind of Source.