Making specifications is taking more and more time; every day an enormous quantity of pages which, for the most part, is written in natural language. However the need to reduce the time needed in the development of the services is a priority. One method is to formalise the maximum number of specifications received. With this in mind, we will try to demonstrate the possibility of a certain automation in the passage from the informal to the formal, by means of methods and proven tools, available to assist an expert in specifications. For this end we propose a process of formalisation which relies on an intermediary representation of the specifications with the formalism of conceptual graphs before arriving at a formal description in Z of the initial specification.