A social network consists of a set of actors and a set of relationships between them which describe certain patterns of communication. Most current networks are huge and difficult to analyze and visualize. One of the methods frequently used is to extract the most important features, namely to create a certain abstraction, that is the transformation of a large network to a much smaller one, so the latter is a useful summary of the original one, still keeping the most important characteristics. In the case of a social network it can be achieved in two ways. One is to find groups of actors and present only them and relationships between them. The other is to find actors who play similar roles and to construct a smaller network in which the connection between the actors would be replaced with connections between the roles. Classifying actors by the roles they are playing in the network can help to understand 'who is who' in a social network. This classification can be very useful, because it gives us a comprehensive view of the network and helps to understand how the network is organized, and to predict how it could behave in the case of certain events (internal or external).