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/impl/AttributeFactoryImpl.java
case AttributePackage.SORT_OPTION_OBJECT :
				return convertSortOptionObjectToString( eDataType,
						instanceValue );
			case AttributePackage.STRETCH_OBJECT :
				return convertStretchObjectToString( eDataType, instanceValue );
			case AttributePackage.STYLED_COMPONENT_OBJECT :
				return convertStyledComponentObjectToString( eDataType,
						instanceValue );
			case AttributePackage.TICK_STYLE_OBJECT :
				return convertTickStyleObjectToString( eDataType, instanceValue );
			case AttributePackage.TRIGGER_CONDITION_OBJECT :
				return convertTriggerConditionObjectToString( eDataType,
						instanceValue );
			case AttributePackage.TRIGGER_FLOW_OBJECT :
				return convertTriggerFlowObjectToString( eDataType,
						instanceValue );
			case AttributePackage.UNITS_OF_MEASUREMENT_OBJECT :
				return convertUnitsOfMeasurementObjectToString( eDataType,
						instanceValue );
			case AttributePackage.VERTICAL_ALIGNMENT_OBJECT :
				return convertVerticalAlignmentObjectToString( eDataType,
						instanceValue );
			default :
				throw new IllegalArgumentException( "The datatype '" + eDataType.getName( ) + "' is not a valid classifier" ); 
		}
	}
	/**
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 */