Interesting this post where Bruce Schneier, the famous security technologist, offers a personal interpretation of a possible social data taxonomy centered on trust level. A valid point of view for both users and administrators. Internet can become very unpredictable, uncontrollable, and then cause unpleasant situations, even dangerous, so it’s always good to have perfectly clear in mind WHAT is going to end into a social network (and not only) and HOW this will be controlled and eventually made available.

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.

Mechanical Poetry offers here a different classification centered instead on the destination of data.