Metadata provides information about some other, primary, data. It is data about data. For example there may be a primary file containing a song and a separate metadata file containing the name of the song, the name of the primary file, a URL to download the primary file, and lyrics. In the context of P2P, metadata usually comes up for one of two reasons:
- it tends to be smaller and thus easier to move than primary data, and
- undirected routing uses functional descriptions of resources rather than network addresses - functional descriptions and metadata are closely related.
The Dublin Core project is developing standardized metadata formats.