Re: Handling multiple rdfs:ranges

The interpretation of rangeIncludes etc., becomes easier if one hand-waves
in a simple temporal context .

A canonical reference oracle (iming danbri) accepted the assertion that the
set of rangeIncludes axioms could be considered closed for a given version
of schema.org.

The included ranges form an anonymous unionOf; the effective range is the
conjunction of this anonymous range with all other range assertions
applicable to property, whether through assertions or by inheritance.

Inferences from assertions in a document using schema.org semantics should
be made with respect to the version of the schema that existed at the time
the assertions were made.
This behavior roughly corresponds to the behavior of the various sdo
sponsors validators.

This assumption allowed for relatively simple mapping to OWL (literal types
were just converted to classes, with magic boxing/unboxing).

Generating named classes for the anonymous unions and computing the class
hierarchy revealed a good bit of hidden structure, and also uncovered
anomalies caused by errors.

One interesting idiom that initially made no sense until it is explained is
the use of ranges that are (Text or URL), where URL is a subclass of Text.
This generally indicates an identifier of some kind, where the URL is in
principle pointing to a named individual.

What makes this interesting is that there is no ready way in OWL to
restrict the range of an object property to be a named individual, since
that distinction is purely syntactic. It's easy enough to sort of handle
this poorly (checking for unacceptable anonymous individuals in input,
generating different individual assertions, and discarding inferred anons
in post).  It's difficult to handle this cleanly without bringing up a
whole raft of UNA issues (and CWA issues if cardinality constraints are
around).

Simon
On Feb 23, 2016 2:53 PM, "Peter F. Patel-Schneider" <pfpschneider@gmail.com>
wrote:

> On 02/23/2016 09:12 AM, Reto Gmür wrote:
> >
> [...]
> >> Without any official formal semantics for schema.org or other guidance
> >> from
> >> the schema.org people we are reduced to considering the meaning of
> >> English
> >> phrases on the schema.org website.
> >
> > Could it be triples all the way down? Doesn't the justification chain
> > typically ends at some definitions in natural language?
>
> Well, maybe.  There is some stuff that has been machine-validated.  (Which
> then makes the basis some computer code, I guess.)
>
> One big reason for formal semantics is to ground on something that is quite
> precise.  Grounding on simple model theories is useful, I think, because
> there
> is very little wiggle room left in the definitions and constructions, even
> though there is, as you say, still a natural language component that has
> to be
> considered even if the natural language is some language that
> mathematicians
> use to communicate with each other.
>
> >> Worse, the phrases used there are generally quite informal.
> >
> > This makes it difficult indeed.
> >
> > Reto
>
> peter
>
>
>