This paper presents Matelas, a B predicate calculus definition for social networking, modelling social-network content, privacy policies, social-networks friendship relations, and how these relations effect users’ policies. The work presented in this paper is part of an ongoing work that aims at using several formal methods tools and techniques to develop a full-fledged social-network service implementing stipulated policies. Although we employed Atelier B to write Matelas, plans are to port it to Event B and to use Rodin to implement the social-network application.