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
/**
	 * Returns the meta object for enum '{@link org.eclipse.birt.chart.model.attribute.AxisType <em>Axis Type</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for enum '<em>Axis Type</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.AxisType
	 * @generated
	 */
	EEnum getAxisType( );
	/**
	 * Returns the meta object for enum '{@link org.eclipse.birt.chart.model.attribute.ChartDimension <em>Chart Dimension</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for enum '<em>Chart Dimension</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.ChartDimension
	 * @generated
	 */
	EEnum getChartDimension( );
	/**
	 * Returns the meta object for data type '{@link org.eclipse.birt.chart.model.attribute.ChartType <em>Chart Type Object</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for data type '<em>Chart Type Object</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.ChartType
	 * @model instanceClass="org.eclipse.birt.chart.model.attribute.ChartType"
	 *        extendedMetaData="name='ChartType:Object' baseType='ChartType'" 
	 * @generated
	 */
	EDataType getChartTypeObject( );
	/**
	 * Returns the meta object for data type '{@link org.eclipse.birt.chart.model.attribute.DataPointComponentType <em>Data Point Component Type Object</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for data type '<em>Data Point Component Type Object</em>'.