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
* @return the meta object for data type '<em>Leader Line Style Object</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.LeaderLineStyle
	 * @model instanceClass="org.eclipse.birt.chart.model.attribute.LeaderLineStyle"
	 *        extendedMetaData="name='LeaderLineStyle:Object' baseType='LeaderLineStyle'" 
	 * @generated
	 */
	EDataType getLeaderLineStyleObject( );
	/**
	 * Returns the meta object for data type '{@link org.eclipse.birt.chart.model.attribute.LegendBehaviorType <em>Legend Behavior Type Object</em>}'.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @return the meta object for data type '<em>Legend Behavior Type Object</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.LegendBehaviorType
	 * @model instanceClass="org.eclipse.birt.chart.model.attribute.LegendBehaviorType"
	 *        extendedMetaData="name='LegendBehaviorType:Object' baseType='LegendBehaviorType'" 
	 * @generated
	 */
	EDataType getLegendBehaviorTypeObject( );
	/**
	 * Returns the meta object for data type '{@link org.eclipse.birt.chart.model.attribute.LegendItemType <em>Legend Item Type Object</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for data type '<em>Legend Item Type Object</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.LegendItemType
	 * @model instanceClass="org.eclipse.birt.chart.model.attribute.LegendItemType"
	 *        extendedMetaData="name='LegendItemType:Object' baseType='LegendItemType'" 
	 * @generated
	 */
	EDataType getLegendItemTypeObject( );
	/**
	 * Returns the meta object for data type '{@link org.eclipse.birt.chart.model.attribute.LineDecorator <em>Line Decorator Object</em>}'.