The need for a generic solution

What we need therefore is a generic solution to putting metadata into our documents, so that a processor can decipher it without having to know in advance that author and geo.position, for example, apply to different things.

For a number of years the general approach has been that metadata and documents just don't mix--you use RDF/XML for complicated metadata, and you put the actual content in your XHTML documents. But as we've seen with examples like location information, people want to put information about themselves, their companies, and their conferences, right into their documents, avoiding the need to publish separate documents. If we're to allow this, but at the same time avoid relying on the implicit knowledge that we discussed, then a key requirement will be to prise apart when we're talking about 'the document' and when we're talking about some other 'thing'.

The first part of what is needed is to bring some order to URI-space and ensure that if a URI is used to represent a document then it isn't used to represent some other 'thing' like a conference or a car, and likewise, if a URI is used to represent a conference or a car, it is never used to represent a document. The second half of the equation is to use a syntax that is richer than the simple meta element embedding provided by HTML (that we have seen in our previous examples).

The solution to the first problem is the notion of information resources, and to the second is RDFa. Let's look at these two points in turn.