The Minimal Set of Attributes for RDFa

Hi all,

I am trying to figure out an efficient way to determine whether a
given document has valid RDFa in it or not, without having to parse
the entire DOM.

So, for example, is it valid to assume that a document *could* be a
proper RDFa document, if I find a "rel" attribute somewhere in the
DOM? Are there any other attributes that can be used without a "rel"
attribute and still be a valid RDFa document?
In essence, what attributes should comprise this *must have* list of
attributes for an RDFa document?

Oshani