Security expert Bruce Schneier today posts about the taxonomy of social networking data. He describes five types of data:
"1. Service data. Service data is the data you need to give to a social networking site in order to use it. It might include your legal name, your age, and your credit card number.
2. Disclosed data. This is what you post on your own pages: blog entries, photographs, messages, comments, and so on.
3. Entrusted data. This is what you post on other people's pages. It's basically the same stuff as disclosed data, but the difference is that you don't have control over the data -- someone else does.
4. Incidental data. Incidental data is data the other people post about you. Again, it's basically the same stuff as disclosed data, but the difference is that 1) you don't have control over it, and 2) you didn't create it in the first place.
5. Behavioral data. This is data that the site collects about your habits by recording what you do and who you do it with."
The importance of such a taxonomy and the definitions is that it provides a framework for discussing the context of privacy problems and rights.