How do you format keywords in Microdata for a CreativeWork?

Question

I'm working with Microdata and I want to use Schema.org’s keywords for CreativeWork.

The schema specifies that it should be text but do I put each keyword in a separate element with itemprop="keywords" or do I put them all in one keywords element? If I put them all in one element do I use commas as a separator?

Answer 1

You should create an itemprop element for each keyword as follows:

<div itemscope itemtype="http://schema.org/CreativeWork">
  <span itemprop="name">Resistance 3: Fall of Man</span>
  by <span itemprop="author">Sony</span>.
  Keywords:
  <a href="/tags/game/"><span itemprop="keywords">Game</span></a>,
  <a href="/tags/adult/"><span itemprop="keywords">Adult</span></a>
</div>

Answer 2

The definition of Schema.org’s keywords property changed. It now reads:

Keywords or tags used to describe this content. Multiple entries in a keywords list are typically delimited by commas.

So it could look like this in Microdata:

<article itemscope itemtype="http://schema.org/BlogPosting">

  <footer>
    <ul itemprop="keywords">
      <li><a href="/tags/foo" rel="tag">foo</a>,</li>
      <li><a href="/tags/bar" rel="tag">bar</a></li>
    </ul>
  </footer>

</article>

(Example taken from my related answer about semantic markup for tags.)

If you don’t want to have commas visible on the page, you could use a meta element in addition to your normal markup for the tags:

<meta itemprop="keywords" content="foo, bar" />

(It’s allowed to place this meta element in the `body´.)

Answer 3

My reading of the specification leads me to the conclusion that you can have just one itemprop attribute per property.

In other words, i don't think that creating an itemprop element for each keyword will create a correct microdata syntax.

I would put each keyword in a space-separated list, and use a single itemprop:

  <span itemprop="keywords">
  <a href="/tags/game/">Game</a>,
  <a href="/tags/adult/">Adult</a>
  </span>

or

 <meta itemprop="keywords" content="Game Adult"/>

i am not sure what should be done in case a keyword contains multiple words, since there is nothing in the specification that says how keywords should be separated in the text (i assume by spaces and.or punctuation like comma).

@Lawrence Woodman : could you indicate where you read, in the specification, that it is allowed to have multiple itemprop elements for the same property?