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
return result;
			}
			case AttributePackage.CHART_TYPE :
			{
				ChartType result = ChartType.get( initialValue );
				if ( result == null )
					throw new IllegalArgumentException( "The value '" + initialValue + "' is not a valid enumerator of '" + eDataType.getName( ) + "'" ); 
				return result;
			}
			case AttributePackage.DATA_POINT_COMPONENT_TYPE :
			{
				DataPointComponentType result = DataPointComponentType.get( initialValue );
				if ( result == null )
					throw new IllegalArgumentException( "The value '" + initialValue + "' is not a valid enumerator of '" + eDataType.getName( ) + "'" ); 
				return result;
			}
			case AttributePackage.DATA_TYPE :
			{
				DataType result = DataType.get( initialValue );
				if ( result == null )
					throw new IllegalArgumentException( "The value '" + initialValue + "' is not a valid enumerator of '" + eDataType.getName( ) + "'" ); 
				return result;
			}
			case AttributePackage.DATE_FORMAT_DETAIL :
			{
				DateFormatDetail result = DateFormatDetail.get( initialValue );
				if ( result == null )
					throw new IllegalArgumentException( "The value '" + initialValue + "' is not a valid enumerator of '" + eDataType.getName( ) + "'" ); 
				return result;
			}