Bug 211839 String grouping unit type needs to support interval range.
Build ID: I20071101-2000 As Chart has supported, the String grouping unit type can be set interval range, the interval range means that the string group will base on row count distinction. For instance, let's say we have a,b,c,d,e,f,g , and set interval range to 2, the grouping result should be a,c,e,g. Now it is a requirement that DtE support the grouping type.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/impl/QueryExecutor.java
this.baseQueryDefn = baseQueryDefn;
		this.aggrTable = aggrTable;
		this.session = session;
		logger.exiting( QueryExecutor.class.getName( ), "QueryExecutor" );
	}
	/**
	 * Provide the actual DataSourceRuntime used for the query.
	 * 
	 * @return
	 */
	abstract protected DataSourceRuntime findDataSource( ) throws DataException;
	/**
	 * Create a new instance of data set runtime
	 * 
	 * @return
	 */
	abstract protected DataSetRuntime newDataSetRuntime( ) throws DataException;
	/**
	 * Create a new unopened odiDataSource given the data source runtime
	 * definition
	 * 
	 * @return
	 */
	abstract protected IDataSource createOdiDataSource( ) throws DataException;
	/**
	 * Create an empty instance of odi query
	 * 
	 * @return
	 */
	abstract protected IQuery createOdiQuery( ) throws DataException;