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
* begin-user-doc --> <!-- end-user-doc -->
	 * 
	 * @generated
	 * @ordered
	 */
	int URL_VALUE__BASE_URL = ACTION_VALUE_FEATURE_COUNT + 0;
	/**
	 * The feature id for the '<em><b>Target</b></em>' attribute. <!--
	 * begin-user-doc --> <!-- end-user-doc -->
	 * 
	 * @generated
	 * @ordered
	 */
	int URL_VALUE__TARGET = ACTION_VALUE_FEATURE_COUNT + 1;
	/**
	 * The feature id for the '<em><b>Base Parameter Name</b></em>' attribute.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int URL_VALUE__BASE_PARAMETER_NAME = ACTION_VALUE_FEATURE_COUNT + 2;
	/**
	 * The feature id for the '<em><b>Value Parameter Name</b></em>' attribute.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	int URL_VALUE__VALUE_PARAMETER_NAME = ACTION_VALUE_FEATURE_COUNT + 3;
	/**
	 * The feature id for the '<em><b>Series Parameter Name</b></em>' attribute.