W3C home > Mailing lists > Public > public-schemaorg@w3.org > November 2016

Re: rdfs:domain and refs:range in schema.org

From: Phil Archer <phila@w3.org>
Date: Thu, 24 Nov 2016 12:05:23 +0000
To: public-schemaorg@w3.org
Message-ID: <056946a5-14a4-dff9-8e38-4ad53c4b7d2e@w3.org>
This presents either a problem or an opportunity (and I'd like to know 
which is true).

The opportunity presented by "domainIncludes" is that you can, I think, 
use a property on a class that is not listed as a domain. In something 
I'm doing right now for the European Commission, I want to use 
schema:openingHours on a schema:ContactPoint. Since the domain of 
schema:openingHours 'includes' CivicStructure and LocalBusiness, perhaps 
that's OK? After all, 'includes' suggests it's not an exhaustive list. 
schema:ContactPoint's suggested schema:hoursAvailable property leads to 
a more complex schema:OpeningHoursSpecification that is useful for 
declaring exceptions - and we want to use that too - but it seems overly 
complex for a simple "usually open Monday to Friday 9 - 5" statement.

So here, domainIncludes, as explained by Dan, wins.

But... Martin's example shows that's *not* how it's being used. Rather, 
it's being used as a constraint language, which I regard as a separate 
thing altogether.

If I put a schema:openingHours property on a schema:ContactPoint, the 
structured data tester will say it doesn't understand my data. Does that 
mean my data is invalid for all potential data consumers or just the 
search engines?

If the data is actually invalid then I'd say that rangeIncludes and 
domainIncludes seem to be mis-named. "domainResterictedToOnly" seems 
more honest? Or am I missing something?

Phil


==Dan's reply copied from archive for reference ==

We wanted to leave the flexibility to evolve the schemas incrementally
without breaking "promises" expressed with RDFS's range/domain, and without
adding lots of artificial supertypes to group different types within a
common type.



== Martin's reply Copied from archive for reference ==
Hi Alex:

This is because the semantics of RDFS domain and range constructs 
*imply* additional type membership instead of *constraining* the 
applicability of a property to a class or value.

With RDFS semantics, a domain spec like so

     foo:schoolAttended rdfs:domain foo:Human.

in combination with the statement

     foo:myDog a foo:Dog ;
               foo:schoolAttended "ACME High School".

implies that

     foo:myDog a foo:Human

instead of throwing a constraint violation error.


Also, if a property had multiple classes as its range or domain, you 
have to create many useless complex classes in order to avoid unintended 
type membership inferences:

In RDFS, a domain spec like so

     foo:yearOfBirth rdfs:domain foo:Human, foo:Dog.

in combination with the statement

     foo:myDog a foo:Dog ;
               foo:yearOfBirth 1971.

implies that your dog is a dog and a human:

     foo:myDog a foo:Human, foo:Dog.

i.e. the intersection of being a dog and human, whatever that is.

The only way to avoid this are complex class definitions, like so:

      foo:yearOfBirth rdfs:domain [ a owl:Class;
				     owl:unionOf (foo:Human, foo:Dog) ].

which will create many, many of those useless classes in the ontology 
because of combinatorial effects.

Martin

-----------------------------------
martin hepp  http://www.heppnetz.de
mhepp@computer.org          @mfhepp




 > On 21 Nov 2016, at 16:39, Alex Prut <mail@alexprut.com> wrote:
 >
 > Hello all,
 > I'm looking at the schema.org raw ontology implementation and 
documentation, but I can’t find a reason why the ontology was 
implemented using the schema:domainIncludes and schema:rangeIncludes 
properties, instead of the standard RDFs rdfs:domain and rdfs:range?
 > Thanks,
 > Alexandru Pruteanu (M.Sc. in Computer Science at University of Udine)
 > mail@alexprut.com
 >
-- 


Phil Archer
Data Strategist, W3C
http://www.w3.org/

http://philarcher.org
+44 (0)7887 767755
@philarcher1
Received on Thursday, 24 November 2016 12:05:37 UTC

This archive was generated by hypermail 2.3.1 : Thursday, 24 November 2016 12:05:37 UTC