What is Metadata
What are metadata, RDF, and the Semantic Web?
Metadata is data about data. For example: title, creator, and licensing information. When you choose a license on our website, you get back some metadata (licensing information) encoded in RDF.
RDF (Resource Description Framework) is a framework for metadata. The basic structure of RDF is very simple. There are three parts:
- the subject: a thing, identified by its URL
- the predicate: the type of metadata (like title or creator), also identified by a URL
- the object: the value of this type of metadata (like "The Story of My Life" or 'a person named "John Q. Public"')
Together, these make RDF statements, which are expressed in a language called RDF/XML.
The Semantic Web is the part of the Web available in RDF. The idea behind the concept of the Semantic Web is that when enough pages carry this machine-processable metadata, developers can build tools that take advantage of it.
Among other things, RDF helps different programs talk to each other, reducing the need for users to copy information by hand. Imagine a world where everything had embedded RDF: When buying a plane ticket, for example, you could drag your flight itinerary onto your calendar program to add it to your calendar. You could drag a friend's top-ten songs list onto your music player, and it could try and obtain the songs for you automatically.
RDF can also be used to create more powerful search engines. Right now the only type of question you can ask a search engine is "What pages have these words in them?" When pages include RDF metadata, you will be able to ask more advanced questions like "What's the current temperature in California?" Programs can also use this information, like an alarm clock program that also displayed the current weather or a collage-making program that only used photos with permission.
Finally, metadata can be aggregated across the whole Web. A program could download all the top-ten song lists and, with the help of a pricing guide in RDF, calculate the cost of buying the most popular albums.
Metadata holds a lot of promise, but it won't be useful until people start adding it to their pages. Creative Commons hopes to help promote metadata by making it very easy for people to add metadata to their pages.