Re: Handling multiple rdfs:ranges

Hi Peter,

On 24 February 2016 at 22:39, Peter F. Patel-Schneider <
pfpschneider@gmail.com> wrote:

> My paper has a lot of discussion of schema.org domains and ranges.  The
> paper
> does not refer much to s:rangeIncludes (or s:rangeIncludes) as these IRIs
> are
> not part of schema.org per se.  I view the discussion of domains and
> ranges in
> the paper as relatively complete.
>

I see. Your paper makes things much clearer, even if not official from
schema.org. In schema.org ranges are already disjunctive.


> One problem with domains and ranges in schema.org is their behaviour when
> extra domains and ranges are available. Constructs that are invalid in some
> way without the extra domains and ranges are valid with them. This is, in
> some
> sense, non-monotonic behaviour.
>

I like the way you carefully say "in some sense, non-monotonic behaviour".
In another sense, this is completely monotonic behaviour. In this other
sense, properties are contravariant (just as inputs to functions or data
sent over a channel). Thus to refine the type of a resource you strengthen
the type, using intersection for example; but for properties you do the
opposite, you weaken the type, using union for example. In this way, we can
monotonically refine the schema information to accommodate both new
explicit type information and new range triples.

Despite many helpful pointers, I am still unconvinced from this thread that
there is practical rational behind the decision by the RDF Schema working
group to make property domains and ranges conjunctive rather than
disjunctive. The example given by AZ was unclear until he highlighted he
was also considering female lizards;) However, on the other hand, there are
scenarios where two people state that the range of a property is different
type. E.g., in DBpedia, dbp:subdivisionName is sometimes used with range
int and other times used with URI dbp:Place:

  dbpedia:Rockmart,_Georgia dbp:subdivisionName 1872 .
  dbpedia:Rockmart,_Georgia dbp:subdivisionName
dbpedia:Polk_County,_Georgia .

This can easily happen with more than one person contributing data, as
intended on the Web of Data. However, if both authors separately
contributed respective schema information for the range, then under the
conjunctive semantics any triple in which dbp:subdivisionName appears as
the property is inconsistent. In contrast, under a disjunctive semantics
both contributors datasets can be used together -- even without prior
coordination -- as expected on the Web of Data. I am possibly opening a
Pandora box here, by using an int along with a URI in this example; but
similar weaker examples using URIs only and resulting in nonsensical
conjunctions instead of full blown inconsistencies can be constructed.

Using owl:unionOf, the above problem can be resolved, but only with
concious coordination between the two contributors and also by stepping
slightly out of RDF Schema.

Of course, a standard is a standard, so I should say no more. However, if
anyone does have a strong either practical or model theoretic case for the
conjunctive handling of domains and ranges in the RDF Schema spec then I
would be most interested to hear at any point.

Kind regards,

Ross