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 -->
	 * @return the meta object for enum '<em>Tick Style</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.TickStyle
	 * @generated
	 */
	EEnum getTickStyle( );
	/**
	 * Returns the meta object for enum '{@link org.eclipse.birt.chart.model.attribute.TriggerCondition <em>Trigger Condition</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for enum '<em>Trigger Condition</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.TriggerCondition
	 * @generated
	 */
	EEnum getTriggerCondition( );
	/**
	 * Returns the meta object for enum '{@link org.eclipse.birt.chart.model.attribute.TriggerFlow <em>Trigger Flow</em>}'.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @return the meta object for enum '<em>Trigger Flow</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.TriggerFlow
	 * @generated
	 */
	EEnum getTriggerFlow( );
	/**
	 * Returns the meta object for enum '{@link org.eclipse.birt.chart.model.attribute.UnitsOfMeasurement <em>Units Of Measurement</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for enum '<em>Units Of Measurement</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.UnitsOfMeasurement
	 * @generated
	 */