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
EEnum getUnitsOfMeasurement( );
	/**
	 * Returns the meta object for enum '{@link org.eclipse.birt.chart.model.attribute.VerticalAlignment <em>Vertical Alignment</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for enum '<em>Vertical Alignment</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.VerticalAlignment
	 * @generated
	 */
	EEnum getVerticalAlignment( );
	/**
	 * Returns the meta object for data type '{@link org.eclipse.birt.chart.model.attribute.ActionType <em>Action Type Object</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for data type '<em>Action Type Object</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.ActionType
	 * @model instanceClass="org.eclipse.birt.chart.model.attribute.ActionType"
	 *        extendedMetaData="name='ActionType:Object' baseType='ActionType'" 
	 * @generated
	 */
	EDataType getActionTypeObject( );
	/**
	 * Returns the meta object for data type '{@link org.eclipse.birt.chart.model.attribute.Anchor <em>Anchor Object</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for data type '<em>Anchor Object</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.Anchor
	 * @model instanceClass="org.eclipse.birt.chart.model.attribute.Anchor"
	 *        extendedMetaData="name='Anchor:Object' baseType='Anchor'" 
	 * @generated
	 */
	EDataType getAnchorObject( );
	/**