Bas Braams,
I sent your question about the inadmissible relationships section of ISO 25964 on to Jack Bruce, one of the thesaurus experts at Access Innovations. He came back with the comments below, and he also suggests a course of action for clearing up some of the terms if that is desired.
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Section 14.3 of ISO 25964-1 states that "If two terms or concepts already have one of the basic relationships, no other basic relationship between the same terms or concepts is admissible". The validation check must detect whether Term A and Term B contain a proper relationship between one another.
If Concept A (Binary stars) has Concept B (Multiple stars) as a broader term, then Concept B cannot have Concept A as a broader term simultaneously. This would create an infinite recursion within the hierarchy, which is the main concern for the validation check. A recursion would extend endlessly throughout the vocabulary.
(ex. Astronomical objects > Star systems > Multiple star systems > Multiple stars > Binary stars Multiple stars > Binary stars > Multiple stars > Binary stars > ... )
Additionally, if one term subsumes the other, then an associative relationship (RT) would not be appropriate between the two.
The example given in 14.3 appears to be much more strict in terms of functionality and checking for valid relationships. The line "If Concept A has BT Concept B, none of the concepts in the BT hierarchy above Concept B should be admissible as BT, NT or RT of Concept A" suggests that terms in the hierarchy above Multiple stars must not contain Binary stars as a narrower term or related term. It may be impossible to detect whether or not the RTs would be appropriate.
In the UAT, examples 2,3, and 4 do not create a recursion. Binary stars do not contain Multiple stars, Stars, or Binary systems as a Narrower Term. However, for a reviewer of the thesaurus, it may or may not be appropriate for the term Binary stars and Multiple stars to be nested under Stars. Removing Stars as a Broader Term for Binary stars and Multiple stars would resolve the issue this reviewer is facing. For polyhierarchy, it may be difficult to determine whether or not these terms should be "aunts and uncles" of themselves, but if it is jarring to a reviewer, then I would suggest removing them. If their relationship causes a recursion, then they must be removed immediately.
There are exceptions (as stated by 14.1 General section of ISO 25964-1), but I believe that the important factor for 14.3(g) is to prevent an infinite recursion within the hierarchy. The relationships may be invalid based on the concepts themselves (such as a misplaced term), but I don't think these polyhierarchical terms are of critical importance. It may be easier to make the suggestion stated above and move on to the other sections of the thesaurus.
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