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
* <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.TriggerFlow
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getTriggerFlowObject()
	 * @generated
	 */
	int TRIGGER_FLOW_OBJECT = 104;
	/**
	 * The meta object id for the '<em>Units Of Measurement Object</em>' data type.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.UnitsOfMeasurement
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getUnitsOfMeasurementObject()
	 * @generated
	 */
	int UNITS_OF_MEASUREMENT_OBJECT = 105;
	/**
	 * The meta object id for the '<em>Vertical Alignment Object</em>' data type.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @see org.eclipse.birt.chart.model.attribute.VerticalAlignment
	 * @see org.eclipse.birt.chart.model.attribute.impl.AttributePackageImpl#getVerticalAlignmentObject()
	 * @generated
	 */
	int VERTICAL_ALIGNMENT_OBJECT = 106;
	/**
	 * Returns the meta object for class '{@link org.eclipse.birt.chart.model.attribute.ActionValue <em>Action Value</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for class '<em>Action Value</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.ActionValue
	 * @generated
	 */
	EClass getActionValue( );