norman.walsh.name: Comments on /2004/04/02/notinrdf

Comment 1 on /2004/04/02/notinrdf

2004-04-03T02:38:42Z

I would interpret that as saying, "If a resource is a tree and the color of its leaves is unknown, then it has green leaves."

If you want to state that a particular true does not have green leaves, I think something like this would work:

:redMaple rdf:type [ a owl:Class ; owl:complementOf [ a owl:Restriction ; owl:onProperty desc:leaves ; owl:hasValue "green" ] ] .

Meaning, ":redMaple belongs to the complement of the class of things with green leaves."

Comment 2 on /2004/04/02/notinrdf

2004-04-04T03:06:35Z

How about this... suppose you declare a prefix/namespace like:

@prefix desc: <http://example.org/rdfschema/tree/attributes#> . @prefix descNot: <http://example.org/rdfschema/tree/attributes#!> .

"descNot" is the same as the "desc" namespace you originally gave, except that it includes a "!" after the hash. Generated URI references are still legal. In other words, you end up with something like:

http://example.org/rdfschema/tree/attributes#!leaves

Now, for an engine that understands the negation syntax, this would be detectable. If it also understood the vocabulary, detection of such URI references could be easily optimized.

If the engine doesn't understand the syntax, regardless of whether it understands the vocabulary or not, it will just be treated as an unrecognized predicate, like any other, and handled appropriately.

Or has all this been tried before? Oh, and if you are shaking your head, I should point out that I am relatively new to RDF. If you are nodding, then ignore that last bit. :)

Comment 3 on /2004/04/02/notinrdf

2004-04-04T22:08:26Z

Another good look at negation in a purely logical, semantic construction is the constructed language lojban.

There are a variety of ways to negate things in lojban, depending on what it is that you're negating.

Doing a quick google search for "lojban negation" yields me:

someone mentioning the conceptual roots of lojban negation: http://balance.wiw.org/~jkominek/lojban/9508/msg00011.html

a quick summary of lojbanic negation: http://balance.wiw.org/~jkominek/lojban/9105/msg00109.html

and lastly, the chapter in the reference grammar on the subject: http://www.lojban.org/publications/reference_grammar/chapter15.html

I'm sure there are many other good resources out there on the subject, but this is one nice example of prior-thought on the subject.