RE: siteData-36: strawman + httpRange-14 [ "Resource-Type:" ]

> ... a point of RDF datatyping is that a property's
> _datatype_ is a function of the property, so that we might have:

Err... no. Unfortunately, it's not. There is no way to do
RDF datatyping in terms of property-specific knowledge.

RDF Datatype provides no machinery whatsoever for global
datatyping, such that a specific datatype can be associated
with a property and that datatype is used to interpret
non-explicitly datatyped literal values.

There was heavy debate for well over a year about this, and
there are outstanding objections to the fact that one
cannot say "all values of foo:date are of type xsd:date".

The following is semantically invalid

   foo:date rdfs:range xsd:date .
   #bar foo:date "2003-03-03" .

because the interpretation of the literal "2003-03-03"
is the literal string "2003-03-03" and *not* the date
March 3, 2003, and there is *no* way to change the
meaning of that value based on any knowledge about the
property in question.

Sucks, doesn't it?   ;-)

> site:creation-date
> site:last-modification-date
> site:backup-date
>
> etc. each of which are dates. 

Only if each and every value of those properties are
explicitly typed as dates. No statements about the
properties themselves will affect the datatyping of
their values in any way.

> Now suppose we restrict the 
> _domain_ of the
> property to apply to sites i.e.
> 
> site:last-modification-date rdfs:domain :site .
> 
> well then it becomes quite simple, anytime we see:
> 
> <> site:last-modification-date "2003-03-05" .
> 
> we _can infer_ that <> is a :site!

True, but you won't be able to infer that the value
"2003-03-05" is a date value. It's not. And any interpretation
of that value as anything but the string "2003-03-05" is
in direct conflict to the meaning expressed by the RDF,
and for a SW application, a no no.

If you *want* a date, you have to say

   <> site:last-modification-date "2003-03-05"^^xsd:date .

and you have to specify the datatype for *every* instance of
*every* value.

Patrick

--
Patrick Stickler, Nokia/Finland, (+358 40) 801 9690, patrick.stickler@nokia.com

Received on Wednesday, 5 March 2003 11:13:45 UTC