Connecting Social Content Services using FOAF, RDF and REST
The pressure for information to be free, is translating into pressure for sites to expose open services for users to interact with. Similar pressures are leading to standardisation of data formats; web services alone aren’t enough the data must be portable and easily exchangeable. XML and RDF are both core technologies that facilitate this exchange, with specific vocabularies, such as FOAF (description of users) and RSS (syndication of content) addressing particular needs.
An interesting paper on online social networks