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copied!<p><code>property</code> vs. <code>rel</code>:</p> <p>Both attributes indicate a <em>predicate</em> of a triple, e.g. <code>rel="http://purl.org/dc/terms/creator</code>, which is the predicate <code>... has as a creator: ...</code>.</p> <p>The difference is, from where they take their <em>object</em>. Slightly simplified, the rules for <code>property</code> are: The object is taken ...</p> <ul> <li>from a valid <code>content</code> attribute or, if this is not present in the tag,</li> <li>(if no <code>datatype</code> attr is present in the tag:) from a valid <code>resource</code> attribute or, if this is not present in the tag,</li> <li>(if no <code>datatype</code> attr is present in the tag:) from a valid <code>href</code> attribute or, if this is not present in the tag,</li> <li>(if no <code>datatype</code> attr is present in the tag:) from a valid <code>src</code> attribute or, if this is not present in the tag,</li> <li>from the inner content of the element started by the tag.</li> </ul> <p>Slightly simplified, <code>rel</code> differs in two aspects:</p> <ul> <li>It takes its object only from a <code>resource</code> or a <code>href</code> or a <code>src</code> attribute.</li> <li>It takes its object not only from an attribute <em>of the same tag</em>, but may also take it from descendant tags. The whole mechanism is called "chaining": "This is the main difference between @property and @rel: the latter induces chaining, whereas the former, usually, does not." <a href="http://www.w3.org/TR/rdfa-syntax/#h3_s_chaining" rel="nofollow">1</a> Usually, but <code>property</code> can induce chaining if used with <code>typeof</code> (cf. <a href="http://www.w3.org/TR/rdfa-core/#chaining-with-property-and-typeof" rel="nofollow">2</a>).</li> </ul> <p><code>about</code> vs <code>resource</code>:</p> <p><code>about</code> is the attribute to indicate the <em>subject</em> of a triple. The rules for <code>resource</code> are more complicated: It may indicate a subject or an object, and chaining plays a role here, too.</p> <p>IMHO, chaining is the most complicated and confusing part of RDFa (and does not give you more than syntactic sugar). I would avoid chaining. This is possible by avoiding the attributes <code>rel</code>, <code>rev</code>, <code>resource</code> and <code>typeof</code>, which brings some further simplification at the same time. Thus, I use only the following attributes:</p> <ul> <li><code>about</code> for the <em>subject</em></li> <li><code>property</code> for the <em>predicate</em></li> <li><code>content</code> or <code>href</code> or <code>src</code> (or the inner content of the element) for the <em>object</em>, following the rules outlined above</li> <li><code>lang</code> for a language tag for object literals, e.g. <code>lang="en"</code></li> <li><code>datatype</code> for a datatype tag for object literals</li> <li><code>prefix</code> (but only once in a document), so that I can abbreviate URLs by prefixing, e.g. <code>property="dc:creator"</code></li> <li><code>vocab</code> (rarely and at the most once in a document), so that I can abbreviate URLs implicitly, e.g. <code>property="creator"</code>.</li> </ul> <p>(And I use the tag <code><base href="..."></code> to indicate the URL base value of the document.)</p> <p>This is a strict, safe, easy-to-use and easy-to-parse subset of RDFa and allows to express any triple you want.</p>

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