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

From: Jarno van Driel <jarnovandriel@gmail.com>
Date: Mon, 9 Jun 2014 23:13:48 +0200
Message-ID: <CADK2AU26J4s+3n0JT6DT-e_RnnobeHKcteuwK5A-rnffwjWDzQ@mail.gmail.com>
To: Markus Lanthaler <markus.lanthaler@gmx.net>
Cc: W3C Web Schemas Task Force <public-vocabs@w3.org>
"...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


> "...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?


2014-06-09 21:50 GMT+02:00 Markus Lanthaler <markus.lanthaler@gmx.net>:

> On Monday, June 09, 2014 9:29 PM, Jarno van Driel wrote:
> > But what about the two entities with the same @itemid?
> >
> > And what about fragment identifiers (#), how does schema.org look at
> > those?
>
> The value of itemid will always be resolved against the base URL. So, if
> your document lives at http://example.com/document the "global
> identifier" will be http://example.com/document#fragment
>
>
> > The Microdata spec says "...It is up to such specifications to define
> > whether multiple items with the same global identifier (whether on the
> > same page or on different pages) are allowed to exist, and what the
> > processing rules for that vocabulary are with respect to handling the
> > case of multiple items with the same ID."
>
> Well, that says it all, doesn't it? From a Microdata perspective, it is
> undefined. Schema.org states [1] that the datamodel is derived from RDF
> Schema. I interpret that as "schema.org is based on RDF's data model". In
> RDF, "multiple items with the same global identifier" do not exist, they
> are all the same "item" (resource) [2]. So, if you use the same itemid for
> different items, all properties would be merged so that you end up with a
> single item. Obviously I don't know for sure what search engines do
> internally with such data but I assume that's what they do.. especially
> since RDFa and JSON-LD are supported as well and they work exactly this way.
>
>
> [1] http://schema.org/docs/datamodel.html
> [2] http://www.w3.org/TR/rdf11-concepts/
>
>
> --
> Markus Lanthaler
> @markuslanthaler
>
>
>
>
>


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*Jarno van Driel*
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Received on Monday, 9 June 2014 21:14:15 UTC

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