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Re: @itemid and URL properties in schema.org

From: Peter Mika <pmika@yahoo-inc.com>
Date: Sun, 06 Nov 2011 15:13:03 +0100
Message-ID: <4EB695EF.8060506@yahoo-inc.com>
To: Gregg Kellogg <gregg@kellogg-assoc.com>
CC: Jeni Tennison <jeni@jenitennison.com>, "public-vocabs@w3.org" <public-vocabs@w3.org>, HTML Data Task Force WG <public-html-data-tf@w3.org>
Hi Gregg,

It is stated in the textual description that 'url', 'image' and in fact 
many other properties (e.g. discussionURL of CreativeWork) must have a 
value of type 'URL'. Microdata doesn't have a schema language, so there 
is no way to formalize this constraint. In OWL, the only way to express 
this constraint is to use a datatype-property: using an object property 
would allow any resource (including bnodes) as value.

Do I see this wrong?


p.s. It's a different matter that the particular syntax (HTML5 + 
microdata) limits the values of particular attributes to URLs.

On 11/5/11 8:03 PM, Gregg Kellogg wrote:
> On Nov 5, 2011, at 11:29 AM, Peter Mika wrote:
>> Hi Jeni,
>>> This is part of the point of my posting about this :) We have a problem here, in that the mapping of properties typed URL to literal values in the schema.org OWL ontology clashes with the assumption in the microdata-to-RDF mapping that we've been developing [1], which assumes that any @href, @src etc provides the identifier of a resource, giving the property an object value rather than a literal value.
>> Thanks, I haven't seen this mapping yet. I'm happy to change the
>> generated OWL file to bring it in line with this mapping.
>> One technical point: this new mapping seems to consistently talk about
>> URI references, while the microdata spec talks about URLs. Further, if I
>> say in the OWL ontology that 'url', 'image' etc. are object-properties,
>> then the value can be any URI. However, the intent is to restrict the
>> publisher to providing URLs. Am I nitpicking?
> The spec does describe URI references, and these might not be valid for schema.org, so this should be stated in your vocabulary (although why HTML5 would not allow international identifiers/locators is another discussion). Also, even though the discussion is on URI references instead of URLs, the HTML5 content model does restricted @href, @src and @data to be URLs. The microdata spec restricts @itemid to be a URL, but not @itemtype or @itemprop (as they are not resolved WRT document base). As some vocabularies may, in fact, want to use IRIs, adding registry info that allows properties to take on these ranges is a way to allow for greater expression of internationalized identifiers using microdata.
> Note the recently raised ISSUE-4 [1], which describes a means of supporting both URIs (could be IRIs) and to use the schema 'url' property as the subject.
> Gregg
> [1] http://www.w3.org/2011/htmldata/track/issues/4
>> Thanks,
>> Peter
Received on Sunday, 6 November 2011 14:13:58 UTC

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