A Question about Diffgram Updates

[bbc]

Hello ;

I would be grateful if someone could answer my question about diffgram
updates

I am using diffgrams to update database records. As you will know,
the <before> tag section references the record to be updated. I
thought it was sufficient that the <before> section only include the
Primary Key(PK) fields of the target record, assuming the PK was
specified in the XSD schema. However in my experience, the <before>
section must include all the fields of the target record (except the
timestamp) for the Update to work correctly. Therefore I am wondering
if I'm doing something wrong. My question is: Is there a way to
reference only the PK in the <before> section, or must all fields of
the target record be included.

Thanks in advance