OWL contains some negative assertions, as Thomas noted. Nothing prevents 
anyone else from negating your negative, however, in that Open World. 
Assuming that we have provenance on statements, then you might be able 
to make sense of two conflicting bits of information.

I've found two vocabularies that do a Boolean negation (Not, as well as 
And and Or):

http://vocab.deri.ie/csp
http://vocab.deri.ie/ppo#

The CSP is used for car models, where there can be hundreds of options 
on a car (color, radio, #doors, gps, etc etc). However, looking at the 
diagram [1] I think it would take me great concentration to figure out 
what they are doing (not to mention their weird use of the term 
"Fluent"). I'm going to look for examples but am not sure how to do that 
- hunt and peck, I guess.

kc
[1] http://vocab.deri.ie/csp#Not

On 9/13/13 6:46 AM, Donald Brower wrote:
> 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]

-- 
Karen Coyle
[log in to unmask] http://kcoyle.net
m: 1-510-435-8234
skype: kcoylenet