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Nesting statements

Mark Birbeck's picture
Submitted by Mark Birbeck on Tue, 2006-05-02 14:15.

In RDFa meta elements can be nested. The normal purpose of this is to make statements about the statement that contains them, such as indicating that the category 'fishing' was added by Jane or that the 4 star rating was given by John:

  <head>
    <meta property="category" content="fishing">
      <meta property="dc:creator" content="Jane Doe" />
    </meta>
    <meta property="rating" content="4">
      <meta property="dc:creator" content="John Doe" />
    </meta>
  </head>

But another use of nested statements is to make a lot of statements about the same resource, and this is achieved by adding an about attribute to the top-level statement. Our mark-up could now look like this:

  <head>
    <link rel="dc:creator" href="#about" />
    <meta about="#author">
      <meta property="foaf:name" content="Mark Birbeck" />
      <meta property="geo:lat" content="43.95" />
      <meta property="geo:long" content="4.833333" />
    </meta>
  </head>

In this small example there's not a lot to choose between this and the first syntax where the about attribute was repeated on each statement. But in a larger example the nested approach is probably easier to manage, as we can see here, where information about the author has been extended to include much of what might be in a person's FoaF file:

  <html
   xmlns:geo="http://www.w3.org/2003/01/geo/wgs84_pos#"
   xmlns:foaf="http://xmlns.com/foaf/0.1/"
   xmlns:dc="http://purl.org/dc/elements/1.1/"
  >
    <head>
      <link rel="dc:creator" href="#about" />
      <meta about="#author">
        <link rel="rdf:type" href="[foaf:Person]" />
        <meta property="foaf:name" content="Mark Birbeck" />
        <meta property="foaf:givenname" content="Mark" />
        <meta property="foaf:family_name" content="Birbeck" />
        <meta property="foaf:mbox_sha1sum"
          content="b8b2922a0d39cd7c7db0b4f65124b4dd2a79fa24" />
        <link rel="foaf:homepage" href="" />
        <link rel="foaf:workplaceHomepage" href="http://www.formsPlayer.com/" />
        <meta property="geo:long" content="4.833333" />
        <meta property="geo:lat" content="43.95" />
      </meta>
    </head>
    .
    .
    .
  </html>
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