Service Oriented Architecture (SOA) is becoming a standard de facto and a solution for defining interoperable architectures. Web Services (WS) platform is one of the most widely accepted implementations of this kind of service architectures. In this context there is a huge amount of specifications for a broad range of topics. This paper is focused on the growing importance of security, the increase of collaboration amongst organizations and the emergent need of modelling SOA and security aspects. This paper presents a modelling framework based on Eclipse platform for modelling and designing securitya spects in SOA and a derivation mechanism in order to automatically generate web service security elements. This approach is illustrated with an example.