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Re: Schema.org in RDF ...

From: Richard Cyganiak <richard@cyganiak.de>
Date: Sun, 12 Jun 2011 15:26:31 +0100
Cc: Linked Data community <public-lod@w3.org>, Michael Hausenblas <michael.hausenblas@deri.org>
Message-Id: <0204B0F4-2D60-4C0C-B227-5C60E9D550F9@cyganiak.de>
To: Pat Hayes <phayes@ihmc.us>
Hi Pat,

On 12 Jun 2011, at 00:33, Pat Hayes wrote:
>>> Nothing is gained from the range assertions. They should be dropped.
>> 
>> They capture a part of the schema.org documentation: the “expected type” of each property. That part of the documentation would be lost. Conversely, nothing is gained by dropping them.
> 
> Let me respectfully disagree. Range assertions (in RDFS or OWL) do *not* capture the notion of "expected type". They state a strict actual type, and cannot be consistently be "over-ridden" by some other information. Which has the consequence that these are liable to be, quite often, plain flat wrong. Which in turn has the consequence that there is something to be gained by dropping them, to wit, internal consistency. They are not mere documentation; they have strictly entailed consequences which many actual reasoners can and will generate, and which to deny would be to violate the RDFS specs. If you don't want these conclusions to be generated, don't make the assertions that would sanction them.

Data on the Web is messy. You cannot reason over it without filtering it first. I think it is useful to document how data publishers are *expected* to use these terms, even if we know that many will -- for good or bad reasons -- use them in *unexpected* ways.

> For documentation, use the structures provided in RDFS for documentation, such as rdfs:comment.

rdfs:comment is for prose. We explicitly know the “expected types” of properties, and I'd like to keep that information in a structured form rather than burying it in prose. As far as I can see, rdfs:range is the closest available term in W3C's data modeling toolkit, and it *is* correct as long as data publishers use the terms with the “expected type.”

Best,
Richard
Received on Sunday, 12 June 2011 14:27:01 UTC

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