Kendra Initiative Wiki: Is A And Has A

The two key operations we need to start specifying things are is a and has a.

To say that X is a Y, is that it is an instance of, or a subclass of, a class Y.

To say that X has a property Y means that statements of the form "X Y z" are valid.

But using the rdfs:domain notation runs into problems: as I undertand it, if there is more than one statement using rdfs:domain for a predicate, any objects for which that predicate is valid must belong to all the domain classes.

Quoting from the spec at http://www.w3.org/TR/rdf-schema/#ch_domain :

: "Where a property P has more than one rdfs:domain property, then the resources denoted by subjects of triples with predicate P are instances of all the classes stated by the rdfs:domain properties."

So, if we say

  person has_a weight

and

  non-person has_a weight

we end up with the problem that any x with a weight muse be both a person and a non-person.

Perhaps we can get round this with a formulation like:

  person has_a person-weight
  non-person has_a non-person-weight

and

  person-weight = weight
  non-person-weight = weight

Hmm. I think I'll be sitting down with the OWL definitions for a bit longer.

Another way around this is:

  person is_a PHYSOB
  non-person is_a PHYSOB
  PHYSOB has_a weight

and use inheritance...

But then we have to get all hierarchies right from the beginning...

Third thinks:

 owl:allValuesFrom?

may be what is needed here.

Daniel thinks:

How about loosely coupling with RDF? The more I hear the more I see we could get sucked into a quagmire with RDF.

Perhaps we should concentrate on getting the system to work with itself. We could end up building something that is far more useable than RDF - perhaps. Then just have a concept of translating to and from RDF.

Hmmm...?

OK, let's have

 kendra:has_a

and sort out the detailed semantics later. To do this, we may need to have some way of (perhaps) generating an intermediate property tag, as per discussion above: this has to be done in a consistent way across different data-stores, though.

Cool!

See? Now this wiki is behaving like a forum. See my earlier [rant].