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

From: Markus Lanthaler <markus.lanthaler@gmx.net>
Date: Mon, 9 Jun 2014 20:57:21 +0200
To: "'W3C Web Schemas Task Force'" <public-vocabs@w3.org>
Message-ID: <057c01cf8414$a6d87650$f48962f0$@gmx.net>
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 URL

> Now I've tried to look for info about @itemid on 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.

> What is 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 http://example.com/CorporationPerson

>       <a itemprop="url" href="http://www.example.org">www.example.org</a>
>   </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... I think you get the idea.


Markus Lanthaler
Received on Monday, 9 June 2014 18:57:55 UTC

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