How to access "Part of" in a worksheet?

Hello,

I need to open a worksheet in my code in order to export this data later. In my code, the associated Function and the assosiated Location is reachable. But I cannot access the "Part of" attribute.

            var partList = selElement.OpenWorksheet(filter, WorksheetOpenBehavior.Deep, new List<AttributeId>()

            {

                //AttributeId.PartOf, // non existing attribute qualifier

                AttributeId.Designation,

                AttributeId.CompleteAssociatedFunction,

                AttributeId.CompleteAssociatedLocation,

            });

Why is this attribute not reachable from here? Could I at least load the FullName here where I could truncate the Designation from? If I get my data by collecting the parents names: How would I fake an AttributeId which is needed for my OpenWorkSheet routine?

Thanks for your help.
Peter