This paper describes the general framework and some details of the ODISSEA approach to conceptual modelling and design of information systems. We use a logic-based language for the specification of conceptual models and apply extensively logic-based techniques for the generation of a system design from a conceptual model. The main originality of our work is that our language is based on the deductive approach to conceptual modelling, instead of the usual operational approach. Deductive conceptual models (DCM) show a number of significant advantages, but are much more difficult to design and implement. We deal with the problem of generating a design for a given DCM. We present a new, formal method for generating transactions from a DCM. The method uses the SLDNF proof procedure and can be implemented in Prolog environments.