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

From: Laura Dawson <Laura.Dawson@bowker.com>
Date: Mon, 9 Jun 2014 19:36:27 +0000
To: Jarno van Driel <jarnovandriel@gmail.com>
CC: Markus Lanthaler <markus.lanthaler@gmx.net>, W3C Web Schemas Task Force <public-vocabs@w3.org>
Message-ID: <CFBB846C.72534%laura.dawson@bowker.com>
It is admittedly more difficult on the web where entities¡¯ IDs can be dereferenced to multiple locations. This is where the DOI might come in handy, as it is a single identifier with multiple resolution points.

For fragment identifiers, that¡¯s a tougher call. I can¡¯t think of what their utility would be, but that¡¯s a failure of my own imagination. ;)

From: Jarno van Driel <jarnovandriel@gmail.com<mailto:jarnovandriel@gmail.com>>
Date: Monday, June 9, 2014 at 3:29 PM
To: Laura Dawson <Laura.Dawson@bowker.com<mailto:Laura.Dawson@bowker.com>>
Cc: Markus Lanthaler <markus.lanthaler@gmx.net<mailto:markus.lanthaler@gmx.net>>, W3C Web Schemas Task Force <public-vocabs@w3.org<mailto:public-vocabs@w3.org>>
Subject: Re: The exact meaning of a 'global identifier' (itemid)

But what about the two entities with the same @itemid?

And what about fragment identifiers (#), how does schema.org<http://schema.org> look at those?

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."

2014-06-09 21:08 GMT+02:00 Laura Dawson <Laura.Dawson@bowker.com<mailto:Laura.Dawson@bowker.com>>:
Coming up through the world of describing books (physical and digital, as
objects and as concepts), the one rule that never let me down is ©øLet the
identifier identify; let the metadata [or, in this case, ontology]
describe.©÷ An ISBN, for example, is just a number - fairly meaningless,
definitely not dereference-able. But it is nonetheless a critical
identifier even as we move to different ways of describing books, for the
simple reason that it was developed to say, ©øThis book is not that book.©÷
The more you can decouple descriptions from identifiers, the more
stability and flexibility your schema will have.

On 6/9/14, 2:57 PM, "Markus Lanthaler" <markus.lanthaler@gmx.net<mailto:markus.lanthaler@gmx.net>> wrote:

>On Monday, June 09, 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'm not sure what exactly you mean by "meaning" but it is just the
>identifier that can be used to reference that specific item (or entity).
>It's similar to a primary key in a database but globally valid as it is a
>> 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.
>That sentence says that what the identifier stands for, is described by a
>vocabulary. If I just give you the identifier
>http://example.com/an/entity it wouldn't tell you much. You need to look
>at the properties, types etc. it is marked up with... and those are
>defined by a vocabulary. In this case here, schema.org<http://schema.org>.
>> What is schema.org<http://schema.org>'s perspective on this:
>Assuming that document was retrieved from http://example.com/document it
>tells you that
>> <body>
>>   <div itemid="CorporationPerson" itemscope
>>        itemtype="http://schema.org/Corporation">
>There's exists "item" of type http://schema.org/Corporation

>(Organization: A business corporation) that is identified with the URL

>>       <a itemprop="url"
>>   </div>
>And it has a property http://schema.org/url (URL of the item) whose value
>is http://www.example.org.

>>   <div itemid="Product" itemscope itemtype="http://schema.org/Product">
>There's also a second item, http://example.com/Product, which is of type
>schema.org/Product.<http://schema.org/Product.>.. I think you get the idea.
>Markus Lanthaler

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

Tel: +31 652 847 608
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Received on Monday, 9 June 2014 19:37:03 UTC

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