W3C home > Mailing lists > Public > public-vocabs@w3.org > June 2014

Re: The exact meaning of a 'global identifier' (itemid)

From: Jarno van Driel <jarnovandriel@gmail.com>
Date: Tue, 10 Jun 2014 01:54:30 +0200
Message-ID: <CADK2AU1kUZyharRKzWFiXHNTfmhD9ssfymX2ovEAbfzHXnsZoA@mail.gmail.com>
To: Gregg Kellogg <gregg@greggkellogg.net>
Cc: W3C Web Schemas Task Force <public-vocabs@w3.org>, Markus Lanthaler <markus.lanthaler@gmx.net>
Thanks for your comments Gregg, I thinks that's the clearest info I've read
about the matter so far. A lot of food for thoughts again.

"it would be nice to get some definitive interpretation from schema.org
>  partners"


+1


2014-06-10 0:09 GMT+02:00 Gregg Kellogg <gregg@greggkellogg.net>:

> \On Jun 9, 2014, at 2:37 PM, Markus Lanthaler <markus.lanthaler@gmx.net>
> wrote:
>
> > On Monday, June 09, 2014 11:14 PM, Jarno van Driel wrote:
> >>> "...So, if your document lives at http://example.com/document the
> >>> "global identifier" will behttp://example.com/document#fragment"
> >>
> >> 1] So this because this is simply how it works then or because that's
> >> how schema.org treats itemid? Now I'm not being a smartass here, I
> >> just really want to understand how this is treated from a schema.org
> >> POV
> >
> > Because it’s defined that way in the Microdata spec:
> >
> >     The global identifier of an item is the value of its element's
> >     itemid attribute, if it has one, resolved relative to the element
> >     on which the attribute is specified. If the itemid attribute is
> >     missing or if resolving it fails, it is said to have no global
> >     identifier.
> >
> >
> >>> "...all properties would be merged so that you end up with a single
> >>> item..."
> >>
> >> 2] That's what I thought as well. Which is supported by the fact the
> >> structured data linter resolves it this way. But both Google's and
> >> Yandex's SDTT don't and there is no info I could find on how the
> >> sponsors look at it. So inconclusive data VS no documentation; What am
> >> I to believe for certain?
> >
> > Only Google, Yandex etc. themselves will be able to tell you what they
> do with such data. Maybe you should formulate your question differently.
> Does it affect you if they do it one way or the other way? In which way
> does it affect you? Does it matter?
>
> Of course, anyone may interpret Microdata however they find useful; it
> would be nice to get some definitive interpretation from schema.org
> partners, but they've (collectively) never been forthcoming on what the
> real semantics of schema.org.
>
> That said, schema.org largely extends RDF Schema, and so, IMO, if you
> treat the interpretation as being consistent with RDF/RDFS, I think you'll
> be in the right direction; this is how the Structured-Data Linter
> interprets it. (if someone has an example where this is NOT the case, I'd
> be quite interested to see it).
>
> When interpreting as RDF, it's useful to look at the Microdata to RDF note
> [1]. This defines @itemid as follows:
>
>         [[An attribute containing a URL used to identify the subject of
> triples associated with this item ...]]
>
> When considered as an RDF subject, we can then infer that each use of the
> same @itemid value does refer, in fact, to the same Resource. This means
> that multiple uses of it will have their property values coalesced to be
> about the same subject resource.
>
> Furthermore, when interpreting @itemid, the algorithm says that if there
> is a global identifier which is an absolute URL, use that as the subject,
> otherwise use a blanknode [2]. It then becomes necessary to find the
> content-model of @itemid, which is defined in the Microdata note [2]:
>
>         [[
>         The global identifier of an item is the value of its element's
> itemid attribute, if it has one, resolved relative to the element on which
> the attribute is specified. If the itemid attribute is missing or if
> resolving it fails, it is said to have no global identifier.
>         ]]
>
> This, @itemid values are interpreted the same way as other HTML attributes
> taking a URL [4]. This is consistent with the way that relative IRIs are
> resolved in other RDF specs, such as RDFa, although with regard to HTML's
> definition of a URL, rather than an IRI. Basically, "foo" is resolved
> relative to the base URL of the document, "#foo" is considered as a
> fragment identifier of that document base, and "/foo" would be considered
> an absolute path within the same domain as the document.
>
> Some examples:
>
> Given the document base <http://example.com/foo/bar>
>
> @itemid="baz" => <http://example.com/foo/baz>
> @itemid="#baz" => <http://example.com/foo/bar#baz>
> @itemid="/baz" => <http://example.com/baz>
> @itemid="http://example.org/baz" => <http://example.org/baz>
>
> Gregg
>
> [1] http://www.w3.org/TR/microdata-rdf/
> [2] http://www.w3.org/TR/microdata-rdf/#generate-the-triples
> [3] http://www.w3.org/TR/microdata/#items
> [4] http://www.w3.org/TR/html5/infrastructure.html#resolving-urls
>
> > --
> > Markus Lanthaler
> > @markuslanthaler
> >
> >
> >
> >
>
>


-- 
*Jarno van Driel*
Technical & Semantic SEO Consultant
8 Digits - Digital Marketing Technologies

Tel: +31 652 847 608
Google+: https://plus.google.com/u/0/+JarnovanDriel
Linkedin: linkedin.com/pub/jarno-van-driel/75/470/36a/
Received on Monday, 9 June 2014 23:54:58 UTC

This archive was generated by hypermail 2.3.1 : Tuesday, 6 January 2015 21:29:42 UTC