Bug 104986 Backgound image uses an absolute path
Currently Chart uses an absolute path to indicate a backgournd image, that may cause the design unusable on other environments. Expected the background image can be definded in multiple ways like in report designer. e.g. URI(absolute path), File(relative path), Embedded Image(Encoded Image Data).
chart/org.eclipse.birt.chart.engine/src/org/eclipse/birt/chart/model/attribute/AttributePackage.java
* @see org.eclipse.birt.chart.model.attribute.DateFormatType
	 * @model instanceClass="org.eclipse.birt.chart.model.attribute.DateFormatType"
	 *        extendedMetaData="name='DateFormatType:Object' baseType='DateFormatType'" 
	 * @generated
	 */
	EDataType getDateFormatTypeObject( );
	/**
	 * Returns the meta object for data type '{@link org.eclipse.birt.chart.model.attribute.Direction <em>Direction Object</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for data type '<em>Direction Object</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.Direction
	 * @model instanceClass="org.eclipse.birt.chart.model.attribute.Direction"
	 *        extendedMetaData="name='Direction:Object' baseType='Direction'" 
	 * @generated
	 */
	EDataType getDirectionObject( );
	/**
	 * Returns the meta object for data type '{@link org.eclipse.birt.chart.model.attribute.GroupingUnitType <em>Grouping Unit Type Object</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for data type '<em>Grouping Unit Type Object</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.GroupingUnitType
	 * @model instanceClass="org.eclipse.birt.chart.model.attribute.GroupingUnitType"
	 *        extendedMetaData="name='GroupingUnitType:Object' baseType='GroupingUnitType'" 
	 * @generated
	 */
	EDataType getGroupingUnitTypeObject( );
	/**
	 * Returns the meta object for data type '{@link org.eclipse.birt.chart.model.attribute.HorizontalAlignment <em>Horizontal Alignment Object</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for data type '<em>Horizontal Alignment Object</em>'.