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 org.eclipse.birt.chart.model.attribute.DataPointComponentType
	 * @model instanceClass="org.eclipse.birt.chart.model.attribute.DataPointComponentType"
	 *        extendedMetaData="name='DataPointComponentType:Object' baseType='DataPointComponentType'" 
	 * @generated
	 */
	EDataType getDataPointComponentTypeObject( );
	/**
	 * Returns the meta object for data type '{@link org.eclipse.birt.chart.model.attribute.DataType <em>Data Type Object</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for data type '<em>Data Type Object</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.DataType
	 * @model instanceClass="org.eclipse.birt.chart.model.attribute.DataType"
	 *        extendedMetaData="name='DataType:Object' baseType='DataType'" 
	 * @generated
	 */
	EDataType getDataTypeObject( );
	/**
	 * Returns the meta object for data type '{@link org.eclipse.birt.chart.model.attribute.DateFormatDetail <em>Date Format Detail Object</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for data type '<em>Date Format Detail Object</em>'.
	 * @see org.eclipse.birt.chart.model.attribute.DateFormatDetail
	 * @model instanceClass="org.eclipse.birt.chart.model.attribute.DateFormatDetail"
	 *        extendedMetaData="name='DateFormatDetail:Object' baseType='DateFormatDetail'" 
	 * @generated
	 */
	EDataType getDateFormatDetailObject( );
	/**
	 * Returns the meta object for data type '{@link org.eclipse.birt.chart.model.attribute.DateFormatType <em>Date Format Type Object</em>}'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the meta object for data type '<em>Date Format Type Object</em>'.