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

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

From: Adrian Giurca <giurca@tu-cottbus.de>
Date: Mon, 09 Jun 2014 23:14:15 +0200
To: Markus Lanthaler <markus.lanthaler@gmx.net>
Cc: 'W3C Web Schemas Task Force' <public-vocabs@w3.org>
Message-Id: <3gnRzt0dGWz10rm6@smtp2.tu-cottbus.de>
Hello, 
Is RDF 1.1 Semantics http://www.w3.org/TR/2014/REC-rdf11-mt-20140225/ the semantics of Schema.org data model?

On 9 Jun 2014 21:50, Markus Lanthaler <markus.lanthaler@gmx.net> wrote:
>
> 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 
>
>
>
>
Received on Monday, 9 June 2014 21:14:57 UTC

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