RDF - the Resource Description Framework - is a de facto metadata language developed by the W3C. Metadata is simply a term for "data about data". Metadata is used in all walks of life - from information in Web pages such as: title, author, and last modified dates; to information about books from online shopping facilities: prices, publisher, availablility. RDF is a common framework enabling people to express this data in such as way as it can be interoperable. By choosing to use this common framework, you get the added benefit that you can use some of the many tools around (RDF parsers and processors) to maintain the data.
There is a dedicated core community working on RDF, and it is very easy to get help on projects, to ascertain how RDF may or may not be able to help in your application scenario. This primer is not intended as a substitute for reading the specifications, or getting to grips with the work currently being done, but it is intended as a valuable resource for enabling you to find out:-
The key principles behind RDF are in fact very simple, and it is relatively easy to port current information models so that they use RDF. It is also just as easy to build new information systems from scratch using RDF.
RDF itself is related to many different academic and business environments and domains, among the groups finding utility in RDF are librarians, logicians, database maintainers, knowledge representation communities, and news/information syndicators.
Enough procastrination; what does RDF "look" like? The following a small chunk of RDF in XML format (don't worry if you don't know what XML is for the time being):-
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns="http://www.w3.org/2000/10/swap/pim/contact#">
<Person rdf:about="http://www.w3.org/People/EM/contact#me">
<mailbox rdf:resource="mailto:em@w3.org"/>
<fullName>Eric Miller</fullName>
<personalTitle>Semantic Web Activity Lead</personalTitle>
</Person>
</rdf:RDF>
This example is just a representation of some simple data which roughly translates as "there is someone called Eric Miller, with the email address em@w3.org, and who is the Semantic Web Activity Lead". Note that there are Web addresses in there - the utility of which we shall explain later on - and some rather obvious things including some "properties" like "mailbox" and "fullName", and the values "em@w3.org", and "Eric Miller".
The advantage of having this information in a machine processable format is that we can link bits of data across the Web. The twist in the plot is that instead of the simple "hyperlinks" that one would find in HTML (the links in the documents), we can link any "thing" to any other "thing". So, instead of talking about Web pages, and sites, we can talk about cars, business, personnel, news events... in fact, anything.
As we continue through the primer, we shall be addressing standard ways of modelling things in RDF, implemeting systems, the relationship between RDF and the "Semantic Web", and discussing further resources and implementation for you to chase up.
Sean B. Palmer