Can I refer to other sites than Schema.org to define itemtypes?

Question

On the Schema.org blog it says that besides using the hierachy on Schema.org, someone can also use external sites like Wikipedia to define an itemprop.

Would it also be correct markup to do the same with an itemtype? So let's say I wanted to make clear that certain content is about a C++ library. Would this be a valid way to do so?

<div itemscope itemtype="http://en.wikipedia.org/wiki/Category:C++_libraries">
C++ library</div>

If so, I would then have no list of assigned possible itemprops for this itemtype. So a new question would arise: what itemprops can I use for itemtypes defined on other sites than Schema.org?

score 1 · Answer 1 · answered Nov 14 '13 at 00:09

You're confusing itemtypes, itemprops and itemids in your question. Your code sample uses itemtype but you refer to the blog post as saying you can use external URIs as itemprops when in fact the blog post is talking about using them as itemids.

The correct Schema.org markup for what you're trying to do would look like this in HTML microdata:

<body itemscope itemtype="http://schema.org/WebPage">
    This page is about <a href="http://en.wikipedia.org/wiki/Category:C++_libraries" itemprop="about">C++ libraries</a>.
</body>

score 1 · Answer 2 · edited May 23 '17 at 12:05

schema.org is a vocabulary.

This vocabulary can be used in Microdata and RDFa.

You can use many more vocabularies with Microdata and RDFa.

So regarding your question in the title:

Can I refer to other sites than Schema.org to define itemtypes?

Yes. But these "sites" would have to define a Microdata vocabulary, i.e., which URIs to use for which types/properties and their definition.

You should never use URIs for types/properties that are not meant to be used for it. Always consider it possible that the webmaster of these URIs might define a vocabulary in the future; it’s likely that your assumed meaning differs from that of the webmaster. Thus: don’t use Wikipedia URIs for Microdata’s itemtype/itemprop attributes (unless Wikipedia decides to publish a corresponding vocabulary).

Can I refer to other sites than Schema.org to define itemtypes?

2 Answers2