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RE: How to avoid that collections "break" relationships

From: Markus Lanthaler <markus.lanthaler@gmx.net>
Date: Sun, 30 Mar 2014 19:51:11 +0200
To: "'Pat Hayes'" <phayes@ihmc.us>
Cc: <public-hydra@w3.org>, "'Peter F. Patel-Schneider'" <pfpschneider@gmail.com>, <public-lod@w3.org>, "'W3C Web Schemas Task Force'" <public-vocabs@w3.org>, "'Dan Brickley'" <danbri@danbri.org>
Message-ID: <00b301cf4c40$a5ee75c0$f1cb6140$@lanthaler@gmx.net>
On Sunday, March 30, 2014 9:14 AM, Pat Hayes wrote:
> On Mar 29, 2014, at 8:10 PM, Peter F. Patel-Schneider wrote:
> > On 03/29/2014 03:30 PM, Markus Lanthaler wrote:
> >> Schema.org doesn't suffer from this issue as much as other vocabularies
> >> do as it isn't defined with RDFS but uses its own, looser description
> >> mechanisms such as schema:domainIncludes and schema:rangeIncludes.
> >> So what I'm really looking for is a solution that would work in
general,
> >> not just for some vocabularies.
> >
> > I would  like to see some firm definition of just how these looser
> > description mechanisms actually work.
> 
> Yes, I agree. Let me put the question rather more sharply. What follows
> from knowing that
> 
> ppp schema:domainIncludes ccc . ?
> 
> Suppose you know this and you also know that
> 
> x ppp y .
> 
> Can you infer x rdf:type ccc? I presume not, since the domain might
> include other stuff outside ccc.

Right

> So, what *can* be inferred about the
> relationship between x and ccc ? As far as I can see, nothing can be
> inferred. If I am wrong, please enlighten me. But if I am right, what
> possible utility is there in even making a schema:domainIncludes
> assertion?

It is a hint as to what might be at the other end. It sets an expectation
for consumers of such data. Similar to how a labeled link on an HTML page
sets an expectation of what you'll find when you follow it. It is not a
contract because in a lot of cases you don't control the target of that
link. RDFS is kind of a contract as it "infects" the target.. even if you
don't control it. It is up to the consumer to trust such assertions or not.


> If "inference" is too strong, let me weaken my question: what possible
> utility **in any way whatsoever** is provided by knowing that
> schema:domainIncludes holds between ppp and ccc? What software can do
> what with this, that it could not do as well without this?

Software can't do too much with unless you start talking about
probabilistics.. the likelyhood to find a schema:Person at the end of a
schema:author link is higher than finding a schema:Event for instance. Other
than that, it can be used to generate documetation as the one shown on
schema.org.


> Having a piece of formalism which claims to be a 'weak' assertion
> becomes simply ludicrous when it is so weak that it carries no content
> at all. This bears the same relation to axiom writing that miming does
> to wrestling.

It clearly provides value IMO. The value, however, is indeed mostly for
humans and not for machines. As are labels, descriptions etc. I don't really
see a problem with this.


--
Markus Lanthaler
@markuslanthaler
Received on Sunday, 30 March 2014 17:51:53 UTC

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