Bug 181121 Model should provide utility method for cube to get correspond dimension key.
In model cube handle, the relation of cube data set and dimension data sets are managed by a series of dimension condition handles.We need model to add utility method so that we can easily get corresponding dimension data set column names according to given cube dimension keys.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/elements/structures/DimensionCondition.java
{
	/**
	 * Name of this structure. Matches the definition in the meta-data
	 * dictionary.
	 */
	public final static String DIMENSION_CONDITION_STRUCT = "DimensionCondition"; 
	/**
	 * The property name of the data set parameters definitions.
	 */
	public static final String PRIMARY_KEYS_MEMBER = "primaryKeys"; 
	/**
	 * Member name of the cached result set(output columns).
	 */
	public final static String HIERARCHY_MEMBER = "hierarchy"; 
	/**
	 * The file name of the included library.
	 */
	protected List primaryKeys;
	/**
	 * The namespace of the included library.
	 */
	protected ElementRefValue hierarchy;
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.report.model.core.Structure#getIntrinsicProperty(java.lang.String)
	 */
	protected Object getIntrinsicProperty( String propName )