Offhand I would say that there is some confusion with tag. Why would a pl function take in something called a rel_id (p_rel_id), and equate that with a tag. In my mind, a tag is a string, but it must refer to something else, and the basic problem is that the field does not have a reference constraint. If it did, then only valid tags could be used, and then you could guarantee that the tag was unique. The pl function takes in a compound primary key, but the tag values are not enforced correctly to allow it to be part of a compound primary key.
So partly this looks like a data model problem which was somehow abused by certain applications. If the data model problem was removed, developers would have discovered that things didn't work very quickly, and would have fixed their code. But the API that was listed above is not necessarily in error. It might be the one correct piece in this, hard to say just yet.
I ran these queries with an old 5.0... version of OpenACS and didn't find any tags = 1, no object_id = 1. So I can't add anything to the meaning of the 1.
