Bug 180189 Support in memory data set cache.
Currently, Design-Time Data Cache is stored on disks. By performance tests using ramdisk, we found that caching in physical memory can improve the performance of RunAndRender by 30%.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/api/DataEngine.java
/**
     * @deprecated Use newDataEngine(Scriptable) instead. Home Dir is no longer used.
     */
    public static DataEngine newDataEngine( Scriptable sharedScope, File homeDir )
    {
        return newDataEngine( sharedScope );
    }
        
    /**
	 * If and only if current mode is DataEngineContext.MODE_PRESENTATION, query
	 * result can be retrieved from report document. Otherwise a BirtException
	 * will be thrown immediatelly.
	 * 
	 * @param queryResultID
	 * @return an instanceof IQueryResults
	 * @throws BirtException
	 */
	public abstract IQueryResults getQueryResults( String queryResultID )
			throws BirtException;
    
	/**
	 * Provides the definition of a data source to Data Engine. A data source
	 * must be defined using this method prior to preparing any report query
	 * that uses such data source. <br>
	 * Data sources are uniquely identified name. If specified data source has
	 * already been defined, its definition will be updated with the content of
	 * the provided definition object.
	 */
	abstract public void defineDataSource( IBaseDataSourceDesign dataSource ) 
			throws BirtException;