Re: Resources with more than one type

----- Original Message -----
From: "Dickinson, Ian J" <Ian_J_Dickinson@hplb.hpl.hp.com>
To: <www-rdf-logic@w3.org>
Sent: Friday, July 13, 2001 1:17 PM
Subject: Resources with more than one type


> In the DAML 2001/3 spec, the way to create a transitive, unique or
> unambiguous DatatypeProperty is as follows:
>   <daml:DatatypeProperty rdf:ID="p">
>     <rdf:type
> rdf:resource="http://www.daml.org/2001/03/daml+oil#UniqueProperty />
>   </daml:DatatypeProperty>
>
> (and equivalently for transitive and unambiguous properties).  Thus p has
> two rdf:type's - daml:DatatypeProperty and daml:UniqueProperty.  Now I
know
> that where a resource has multiple constraints upon it, the general
position
> is to treat them as a conjunction.

More generally, with any pieces of RDF given in the same ___, treat them as
a conjunction.

> Hence, p is a member of the class of
> Properties that are both datatypes and unique.  This kind of thing is done
> elsewhere in DAML, but not usually by overloading rdf:type ... more
commonly
> subPropertyOf is used.
>
> The reason I bring this up is in thinking about API's for DAML.
Typically,
> resources have at most one rdf:type property,

Not in my book.  A type is simply a unary preciate.  If you only have one
type, then that type be daml:Thing which everything is.  Anything
can belong to an unbounded number of Classes.

> and indeed, DAML defaults the
> type to daml:Thing.  So, ordinarily, we can talk about *the* type of an
> object,

No, we can't.  We can ask for the *set* of types which something has
according to
a given set of infromation (eg a document). We can ask perhaps for a type
which the object has which is the more specific, in othr words which implies
all
the other types, if it exists, but this may not be defined.

Saying that someything has type daml:Thing of course means nothing, and I
wish
that people would delete that information from DAML files to save space.
(I have thought of giving cwm a "--duh"  option which removes all 0 content
information
from the store. 0.5  ;-)

> and an API could comfortable support a get/set semantics for *the*
> type.  If, OTOH, rdf:type should always be thought of as multi-valued,
then
> the semantics for the API will have to be modelled on
> adding/removing/listing the types plural, with an attendant increase in
> complexity.

Yes, but there you are.  Presumably you just want the answer to
the query for triples  (rdf:type,  A, x) returning all x.

The axioms for the DAML Properties will typically give more types
when they are applied to many datas, by inferring supertypes etc.

> So, my question is whether unique (transitive, unambiguous) datatypes,
with
> multiple rdf:type's, are the exception or the rule.

I would say the rule.

> If they are the
> exception, is it more reasonable to (a) trap them as special cases in an
> API, or (b) change the spec so that there is a more elegant way of
> expressing the additional semantic qualifiers on datatype properties?
>
> Regards,
> Ian
>
> ____________________________________________________________________
> Ian Dickinson    HP Labs, Bristol, UK    mailto:Ian_Dickinson@hp.com
>

Received on Wednesday, 18 July 2001 23:07:59 UTC