On Thu, 26 Nov 2009 22:30:41 +0100, Tim van Oostrom <t...@depulz.nl> wrote:
Hi, I made a forumpost : http://forums.whatwg.org/viewtopic.php?t=4176,
concerning a possible "microdata specification bug" and a bug in the
james.html5.org microdata extractor.
Comes down to <link/> and <meta/> elements possibly being unfit for use
with the itemscope attribute.
I made an example in the forum post with some nice ubb formatting .
There are some other issues with <link> and <meta> you might want to
review first: [1]
Your second example was:
<div itemtype="http://url.to/geoVocab#country"; itemscope>
<span itemprop="http://xmlns.com/foaf/spec/index.rdf#name";
lang="cn">中華人民共和國</span>
<span itemprop="http://xmlns.com/foaf/spec/index.rdf#name";
lang="en">China</span>
<link itemprop="http://url.to/city"; href="http://url.to/shanghai";
itemscope itemref="city-shanghai" />
<div id="city-shanghai">
<span
itemprop="http://xmlns.com/foaf/spec/index.rdf#name";>Shanghai</span>
<span itemprop="http://url.to/demoVocab#population";>14.61 million
people</span>
<span itemprop="http://url.to/physicsVocab#time";
datetime="2009-11-26 11:43">11:43 pm (CT)</span>
</div>
</div>
By using itemprop+itemscope, you're saying that the property is itself an
item. Also specifying href="http://url.to/shanghai"; does nothing.
<link>, <meta> and any other void elements are usually the wrong choice
for itemprop+itemscope because they don't have child elements, so itemref
is the only way to add properties. What you've accidentally done above is
add the 3 properties of Shanghai to both the top-level item and the
sub-item, see [2] for details. I would rewrite it to something like:
<div itemtype="http://url.to/geoVocab#country"; itemscope>
<span itemprop="http://xmlns.com/foaf/0.1/name";
lang="zh-CN">中华人民共和国</span>
<span itemprop="http://xmlns.com/foaf/0.1/name"; lang="en">China</span>
<div itemprop="http://url.to/whatShanghaiIsToChina"; itemscope
itemtype="http://url.to/geoVocab#city";>
<span itemprop="http://xmlns.com/foaf/0.1/name";>Shanghai</span>
<span hidden itemprop="http://url.to/demoVocab#population";
content="14610000"></span>
<time itemprop="http://url.to/physicsVocab#time";
datetime="2009-11-26T11:43+08:00">11:43 pm (CT)</time>
</div>
</div>
I don't know how you meant for <http://url.to/city> to be used, the
vocabulary at <http://url.to/geoVocab#country> has to define what
properties are valid and their semantics. The itemprop
<http://url.to/whatShanghaiIsToChina> could be lots of things, what you
want is maybe something that means "financial center of" or "largest
city", I don't know. If <http://url.to/shanghai> is a global identifier
for Shanghai you should use itemid.
I don't know what <http://url.to/physicsVocab#time> is, but note that an
exact time isn't very useful without a timezone, so I added the PRC
timezone for you. I'll also note that using traditional Chinese for the
full name of the PRC is an odd choice, so I changed it to simplified
Chinese above.
Marking up the population as "14.61 million people" isn't terribly helpful
if you want a computer to be able to find the city with the biggest
population among several cities, unless your vocabulary defines how to
parse "14.61 million people" into a number, which would be strange. In any
case this is hidden metadata unless you want 14610000 or some other easily
machine-parsable representation to be visible in the page rendering.
Finally, I think <http://xmlns.com/foaf/spec/index.rdf#name> should be
<http://xmlns.com/foaf/0.1/name>. If you're going to use existing
vocabularies like FOAF and want your data to be play nice with the RDF
world, make sure to check that the result of the RDF extraction algorithm
[3] is what you intended. In particular, you probably want to use itemid
where possible and make sure that all your URIs are exactly correct.
Personally, though, unless I could reuse existing vocabularies for every
single item and property, I would only use a full URI for itemtype and
point that to a vocabulary that defines what simpler property names like
"name" and "city" mean and how to convert the vocabulary to RDF.
[1]
http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2009-November/024116.html
[2]
http://www.whatwg.org/specs/web-apps/current-work/multipage/microdata.html#the-properties-of-an-item
[3]
http://www.whatwg.org/specs/web-apps/current-work/multipage/converting-html-to-other-formats.html#rdf
--
Philip Jägenstedt
Core Developer
Opera Software
