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

From: Adrian Giurca <giurca@tu-cottbus.de>
Date: Mon, 09 Jun 2014 21:43:36 +0200
Message-ID: <53960E68.3010701@tu-cottbus.de>
To: Jarno van Driel <jarnovandriel@gmail.com>, W3C Web Schemas Task Force <public-vocabs@w3.org>
Actually things/resources on the Web are identified by URIs (IRIs). URI 
is NOT URL  but they share the same syntax.
  See more on http://www.w3.org/Addressing/

Microdata specification is very clear on @itemid attribute definition: 
http://www.whatwg.org/specs/web-apps/current-work/multipage/microdata.html#global-identifiers-for-items

(you can see, it provides an example where  the value  of @itemid is a URN)

Microdata is a SYNTAX to encode annotations in HTML5. There is no 
semantics behind Microdata annotations.
A Semantic Data extractor would extract the annotations into a Semantic 
Web knowledge representation language (or other kind of language it like 
to process) and usually THIS language may have attached a semantics 
inside the reasoning can be performed.

Schema.org is a collection of classes and properties uniquely identified 
by URL (e.g., http://schema.org/Article or http://schema.org/author ) 
that can be used as annotations inside HTML5 content (eitherextending 
HTML5 with Microdata language or extending with RDFa language or both or 
extending with other future language...)

Schema.org employs a common sense meaning  (you understand that the HTML 
tree annotated with itemtype="htp://schema.org/Article" is the "formal" 
description of what most of the people will name as article. )

A formal meaning, i.e. a  semantics that can be processed by machines is 
not (yet?) a topic for Schema.org.

Regarding your need  to cross reference local annotated  content see 
http://www.whatwg.org/specs/web-apps/current-work/multipage/microdata.html#attr-itemref

or  http://getschema.org/index.php/awards on using @id/@itemref

Regards,
Adrian Giurca

On 6/9/2014 8:24 PM, Jarno van Driel wrote:
> I would like to know if the exact meaning of a Microdata global 
> identifier (itemid) has been documented?
>
> I've been working on some test code to find out what can and cannot be 
> achieved by using @itemid and unfortunately I can't fully wrap my 
> brain around it since the different testing tools end up giving me 
> different results.
>
> Now I've tried to look for info about @itemid on schema.org 
> <http://schema.org> but can't find anything. The only info out there I 
> could find just says it should be documented by the vocabulary itself.
>
> sources:
> http://www.w3.org/TR/microdata/#global-identifier
> https://groups.google.com/forum/#!topic/schemaorg-discussion/YhF2cNGHVZ4 
> <https://groups.google.com/forum/#%21topic/schemaorg-discussion/YhF2cNGHVZ4>
> https://www.w3.org/Bugs/Public/show_bug.cgi?id=13007
> http://lists.w3.org/Archives/Public/public-vocabs/2011Oct/0127.html
>
> During my testing I got the impression the structured data linter is 
> the only tool that gets my markup right, but that's looking at it from 
> an RDFa perspective.
>
> What is schema.org <http://schema.org>'s perspective on this:
>
> <body>
>     <div itemid="CorporationPerson" itemscope 
> itemtype="http://schema.org/Corporation">
>         <a itemprop="url" 
> href="http://www.example.org">www.example.org <http://www.example.org></a>
>     </div>
>
>     <div itemid="Product" itemscope itemtype="http://schema.org/Product">
>         <span itemprop="name">Donald Duck DVD</span>
>         <link itemprop="brand" href="CorporationPerson" />
>         <span itemprop="offers" itemscope 
> itemtype="http://schema.org/Offer">
>             $<span itemprop="price">19.95</span>
>             <meta itemprop="priceCurrency" content="USD">
>         </span>
>     </div>
>
>     <div itemid="CorporationPerson" itemscope 
> itemtype="http://schema.org/Person">
>         <span itemprop="name">Walt Disney</span>
>     </div>
> </body>
>
> note: I'm not looking for @itemref solutions, extra <links> or 
> different order of HTML, those I can come up with myself just fine. I 
> really just want to know the workings of @itemid from a schema.org 
> <http://schema.org> perspective.
>
> Any thoughts?
>
> -- 
> *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/ 
> <http://linkedin.com/pub/jarno-van-driel/75/470/36a/>


-- 
-Adrian
Twitter <http://www.twitter.com/giurca>
LinkedIn <http://www.linkedin.com/in/adriangiurca>
Received on Monday, 9 June 2014 19:44:28 UTC

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