Big Fractal Tangle: dublin core

Probably the most used RDF schema, besides rdf and rdfs, is Dublin Core, a metadata standard established to describe documents. The first thing you should know about Dublin Core is that it has nothing to do with James Joyce or the city in Ireland. This Dublin is in Ohio, which is where some semweb pioneers met in March 1995 to establish the standard. The next thing you should know about Dubin Core is that it's simple and useful.

How so? Well, Dublin Core is a set of fifteen essential things people want to know about a document: its title, its date, its creator, and so on. By defining a shared terminology, the Dublin Core folks have made it possible for smarter searchs, since we can now say, "Give me all stories (type) by James Joyce (creator) about Dublin (subject)".

The fab fifteen are:

dc:title	formal title	Dubliners
dc:subject	category or keyword	Irish Life
dc:description	free-text account	What to do in Dublin when you're dead
dc:source	larger body of work	n/a
dc:relation	pseudo-RDF reference	IsBasisFor: movie The Dead
dc:coverage	time or place covered	Dublin, Ireland
dc:creator	maker of document	Joyce, James
dc:publisher	provider of access	Bantam Books
dc:contributor	those adding their 2 cents	Maddox, Brenda
dc:rights	copyright or the like	public domain
dc:date	date of release	1914
dc:type	document type	Text
dc:format	media type	pdf
dc:identifier	a unique identifier	ISBN:0553213806
dc:language	human language	en

My examples aren't the best. For the real deal, have a look at the usage guide. While it's not always so clear what values to use, at least the predicates are well defined, which is a big benefit.

To use Dublin Core in your RDF, you first declare the namespace as usual. You then use the "dc" predicates as in any other schema.

<!--
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
   xmlns:dc="http://purl.org/dc/elements/1.1/">
   <rdf:Description 
       rdf:about="http://media.salon.com/mp3s/joyce2a.mp3"
       dc:title="Sisters"
       dc:identifier="http://media.salon.com/mp3s/joyce2a.mp3"
       dc:subject="Irish Life and Death"
       dc:description="Walking by Cotter"
       dc:creator="Joyce, James"
       dc:type="mp3"
       dc:contributor="Frank McCourt" />
</rdf:RDF>
-->

The nice thing about Dublin Core is that you can mix it with just about any schema, like the trackback schema I talked about earlier. Another nice thing is that you don't even have to use RDF. Dublin Core works just as well in straight XML or even our old friend HTML:

<meta name="DC.creator" content="Joyce, James">
<meta name="DC.type" content="mp3">

HTML? Why would we want to use HTML? Meta tags are so nineties, man!

Well, whatever your stripe, Dublin Core's got fifteen fuzzy buckets for you, so get annotating. Google will someday thank you for it.