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 #getTooltipValue()
	 * @generated
	 */
	EAttribute getTooltipValue_Delay( );
	/**
	 * Returns the meta object for class '{@link org.eclipse.birt.chart.model.attribute.URLValue <em>URL Value</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for class '<em>URL Value</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.URLValue
	 * @generated
	 */
	EClass getURLValue( );
	/**
	 * Returns the meta object for the attribute '{@link org.eclipse.birt.chart.model.attribute.URLValue#getBaseUrl <em>Base Url</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for the attribute '<em>Base Url</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.URLValue#getBaseUrl()
	 * @see #getURLValue()
	 * @generated
	 */
	EAttribute getURLValue_BaseUrl( );
	/**
	 * Returns the meta object for the attribute '{@link org.eclipse.birt.chart.model.attribute.URLValue#getTarget <em>Target</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for the attribute '<em>Target</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.URLValue#getTarget()
	 * @see #getURLValue()
	 * @generated
	 */
	EAttribute getURLValue_Target( );