Precondition for a successful personalization is the identification of individual users. The characteristics of users in their user profiles are saved and have them again at a later stage can be clearly assigned. When a computer system can, for example, the login to establish the identity of users and thus the profile assignment serve.
An example of the violation of this requirement, the recommendation systems of some personal video recorder, which a number of household members alternately be used without them distinguish them. Those systems based on a new Electronic Program Guide TV content that they can address the needs personalised gifts of the individual household members only partially satisfied.