W3C home > Mailing lists > Public > public-vocabs@w3.org > October 2012

Re: Meaning of property "url"

From: Martin Hepp <martin.hepp@ebusiness-unibw.org>
Date: Wed, 24 Oct 2012 12:02:08 +0200
Cc: Michael Hopwood <michael@editeur.org>, Ed Summers <ehs@pobox.com>, Cord Wiljes <cwiljes@cit-ec.uni-bielefeld.de>, "public-vocabs@w3.org" <public-vocabs@w3.org>
Message-Id: <07EFBE06-FE41-410B-B15D-1549F084414A@ebusiness-unibw.org>
To: Dan Brickley <danbri@danbri.org>
Hi Dan,
If I understand your post correctly, it would not be correct to use http://schema.org/url for pointing from an abstract object (e.g. a product) to the canonical URL of its Web page, or from a person to its main homepage?

We are using foaf:page in many GoodRelations patterns, so it would be crucial to know whether it is correct to use http://schema.org/url for

a) authoritative identifiers for entities (like http://dbpedia.org/resource/John_Lennon or an identifier (!) from Freebase)
b) HTML pages and PDF documents containing descriptions of the objects (like http://en.wikipedia.org/wiki/John_Lennon)

or both.

My current understanding was that 

1. http://schema.org/url can be used for both and that search engines will try to guess the nature of the URI/URL, so you can use it for related pages (and PDFs?) as well as for authoritative Web-scale identifiers, and that

2. itemid in Microdata and about in RDFa can be used for assigning identifiers.

But now you say that itemid and http://schema.org/url are "broadly equivalent", which confuses me.

If that is meant as I read it, then we likely need to add foaf:page and foaf:homePage to schema.org.

Thanks in advance for clarifying this.


On Oct 23, 2012, at 5:25 PM, Dan Brickley wrote:

> A few observations -
> * We want all Things to be identifiable using URI/IRI/URL identifier notations
> * In the HTML5 the specs use 'URL" rather than "URI"; at launch
> Schema.org's primary notation was HTML5 MIcrodata, so we inherit that
> usage. But Schema.org also targets mainstream developers and
> publishers who often are not so familiar with 'URI' or 'IRI', but feel
> they know what an 'URL' is
> See http://developers.whatwg.org/introduction.html#willful-violation
> http://developers.whatwg.org/urls.html
> HTML5's usage of 'URL' is explicitly in terms of URI and IRI and the
> notion of a 'resource'
> * In RDF, we use 'resource' as a synonym for Thing (ie. all things can
> be considered resources), rather than something like
> 'http-accessible-information-object', which seems to be some people's
> reading of the term. I think Schema.org is closer to the 'thing'
> reading.
> * Microdata has an 'itemid' attribute, for Thing identifiers
> (analagous to resource= in RDFa Lite), see
> http://www.w3.org/TR/rdfa-lite/#resource for the RDFa version.
> * The use of schema.org/url is broadly equivalent to using itemid or
> resource attributes from Microdata and RDFa; it takes the items Web
> identifier and expresses it explicitly as a property value.
> * There is plenty of room still for interpretation, best practice,
> clearer guidelines; the "How do we identify real world entities"
> debate is as old as the Web.
> * Schema.org's deployment in mainstream Web content places some
> practical constraints for some publishers; for example, a Movie site
> where a page /person_321/ links to /tvshow-67241/ might have an
> itemprop="actor" (microdata) or property="actor" (rdfa) annotation.
> That's nice and simple, but parsing gives the actor TV show the same
> URI/IRI/URL as the page describing them; i.e. the http-range-14.  A
> more complex site design (markup and identiifers) that gives different
> IDs to pages and entities is of course possible, but it's not clear
> we'd see strong adoption easily.
> So I'd not read too much into 'url'. It's somewhere you can put a Web
> identifier for the thing being described. As conventions for this in
> the Web standards community mature, we should be able to be more
> precise on this.
> Dan
> p.s. http://www.w3.org/wiki/WebSchemas/sameThingAs is somewhat related

martin hepp
e-business & web science research group
universitaet der bundeswehr muenchen

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Received on Wednesday, 24 October 2012 10:02:43 UTC

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