Hello,
I'm not sure how sensible a question this is (it's certainly theoretical), but it cropped up in relation to a rare books cataloguing discussion. Is there a standard or accepted way to express negatives in RDF? This is best explained by examples, expressed in mock-turtle:
If I want to say this book has the title "Cats in RDA" I would do something like:
example:thisbook dc:title "Cats in RDA" .
Normally, if a predicate like dc:title is not relevant to example:thisbook I believe I am right in thinking that it would simply be missing, i.e. it is not part of a record where a set number of fields need to be filled in, so no need to even make the statement. However, there are occasions where a positively negative statement might be useful. I understand OWL has a way of managing the statement This book does not have the title "Cats in RDA" [1]:
[] rdf:type owl:NegativePropertyAssertion ;
owl:sourceIndividual example:thisbook ;
owl:assertionProperty dc:title ;
owl:targetIndividual "Cats in RDA" .
However, it would be more useful, and quite common at least in a bibliographic context, to say "This book does not have a title". Ideally (?!) there would be an ontology of concepts like "none", "unknown", or even "something, but unspecified":
This book has no title:
example:thisbook dc:title hasobject:false .
It is unknown if this book has a title (sounds undesirable but I can think of instances where it might be handy[2]):
example:thisbook dc:title hasobject:unknown .
This book has a title but it has not been specified:
example:thisbook dc:title hasobject:true .
In terms of cataloguing, the answer is perhaps to refer to the rules (which would normally mandate supplied titles in square brackets and so forth) rather than use RDF to express this kind of thing, although the rules differ depending on the part of description and, in the case of the kind of thing that prompted the question- the presence of clasps on rare books- there are no rules. I wonder if anyone has any more wisdom on this.
Many thanks,
Tom
[1] Adapted from http://www.w3.org/2007/OWL/wiki/Primer#Object_Properties
[2] No many tbh, but e.g. title in an unknown script or indecipherable hand.
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Thomas Meehan
Head of Current Cataloguing
Library Services
University College London
Gower Street
London WC1E 6BT
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