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
instanceValue );
			case AttributePackage.DATA_TYPE_OBJECT :
				return convertDataTypeObjectToString( eDataType, instanceValue );
			case AttributePackage.DATE_FORMAT_DETAIL_OBJECT :
				return convertDateFormatDetailObjectToString( eDataType,
						instanceValue );
			case AttributePackage.DATE_FORMAT_TYPE_OBJECT :
				return convertDateFormatTypeObjectToString( eDataType,
						instanceValue );
			case AttributePackage.DIRECTION_OBJECT :
				return convertDirectionObjectToString( eDataType, instanceValue );
			case AttributePackage.GROUPING_UNIT_TYPE_OBJECT :
				return convertGroupingUnitTypeObjectToString( eDataType,
						instanceValue );
			case AttributePackage.HORIZONTAL_ALIGNMENT_OBJECT :
				return convertHorizontalAlignmentObjectToString( eDataType,
						instanceValue );
			case AttributePackage.ID :
				return convertIDToString( eDataType, instanceValue );
			case AttributePackage.INTERSECTION_TYPE_OBJECT :
				return convertIntersectionTypeObjectToString( eDataType,
						instanceValue );
			case AttributePackage.LEADER_LINE_STYLE_OBJECT :
				return convertLeaderLineStyleObjectToString( eDataType,
						instanceValue );
			case AttributePackage.LEGEND_BEHAVIOR_TYPE_OBJECT :
				return convertLegendBehaviorTypeObjectToString( eDataType,
						instanceValue );
			case AttributePackage.LEGEND_ITEM_TYPE_OBJECT :
				return convertLegendItemTypeObjectToString( eDataType,