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At a theoretical level, doesn't the Open World Assumption in RDF rule out outright negations? That is, someone else may know the title, and could assert it in a separate RDF document. RDF semantics seem to conflate unknown with nonexistent. Practically, Esme's approach seems better in these cases. -Don -- Donald Brower, Ph.D. Digital Library Infrastructure Lead Hesburgh Libraries, University of Notre Dame On 9/13/13 8:51 AM, "Esmé Cowles" <[log in to unmask]> wrote: >Thomas- > >This isn't something I've run across yet. But one thing you could do is >create some URIs for different kinds of unknown/nonexistent titles: > >example:book1 dc:title example:unknownTitle >example:book2 dc:title example:noTitle >etc. > >You could then describe example:unknownTitle with a label or comment to >fully describe the states you wanted to capture with the different >categories. > >-Esme >-- >Esme Cowles <[log in to unmask]> > >"Necessity is the plea for every infringement of human freedom. It is the > argument of tyrants; it is the creed of slaves." -- William Pitt, 1783 > >On 09/13/2013, at 7:32 AM, "Meehan, Thomas" <[log in to unmask]> wrote: > >> 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. >> >> --- >> >> Thomas Meehan >> Head of Current Cataloguing >> Library Services >> University College London >> Gower Street >> London WC1E 6BT >> >> [log in to unmask]