268 Chapter 11—Microdata
<a href=http://openweb.cc itemprop=url>openWeb.cc</a>
</div>
</article>11.1.3 The “itemid” Attribute.............................................................
As soon as a microdata structure has an itemtype attribute, items in the dialect
used can be tagged with unique IDs via the itemid attribute. Examples of such
IDs are the ISBN (International Standard Book Number) for books, the EAN (Eu-
ropean Article Number) for identifying products, and the ASIN (Amazon Stan-
dard Identification Number) for orders within Amazon.
Valid values for the itemid attribute are URLs, including Uniform Resource
Names (URN) with the prefix urn:. Using a fictitious vocabulary for describing
books, the tablature of Pat Metheny’s solo album One Quiet Night could be iden-
tified via its unique ISBN number:<div itemscope
itemtype=http://vocab.example.net/book
itemid="urn:isbn:978-0634066634">
<span itemprop=album>One Quiet Night</span> by
<span itemprop=artist>Pat Metheny</span>
(<time itemprop=pubdate datetime=2005-04-01>2005</time>,
<span itemprop=pages>88</span> pages)
</div>11.1.4 The “itemref” Attribute
Often, it is not possible to accommodate all desired microdata information
within one container element. With our blog entry, the itemscope attribute goes
with the surrounding article element, and all associated itemProp attributes
are within the article. If you want to include itemProp attributes outside of the
article elements, you can use itemref attributes. Separated by commas, they
contain a list of IDs of elements also to be searched for microdata contents. The
connection between the itemscope attribute and a container element can then
be removed completely:<article>
<div id=location>
<span itemprop=member>Pat Metheny</span>
</div>
<div id=intro>
<span itemprop=member>Antonio Sanchez</span>
<span itemprop=member>Steve Rodby</span>