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One of the steps making it possible to increase the quality and the reliability of the software executing on distributed systems consists of the use of methods of software engineering that are known as formal. The majority of the formal methods currently existing correspond in fact more to formal specifications languages than to methods themselves. This is due to the fact that the two fundamental aspects which are: the logic of use of the language and the coverage of the software life cycle are not, for the majority, defined. The development by stepwise refinement is one of the means making it possible to define these two aspects. This thesis aims to the definition of the concepts of refinement and implementation of model-oriented formal specifications. It brings a methodological base making it possible to use such a specifications language during a development by stepwise refinements and during the implementation stage. This thesis defines, initially, a theoretical framework for the refinement and the implementation of formal specifications. The main idea consists in associating a contract with each specification. A contract explicitly represents the whole of the properties of the specification which it is necessary to preserve at the time of a refinement of this specification. To show that a concrete specification refines some abstract specification, it is then a matter of showing that the contract of the concrete specification is sufficient to ensure the properties corresponding to the contract of the abstract specification. The second part of this thesis consists in applying this theoretical framework in the context of the CO-OPN/2 language. CO-OPN/2 is an object-oriented formal specifications language founded on algebraic specifications and Petri nets. Thus, definitions of the concepts of contracts, refinement and implementation are proposed for this language. The contracts are expressed using the Hennessy-Milner temporal logic (HML). This logic is used in the theory of test provided with language CO-OPN/2. Thus, the verification of the contractual properties, as well as the verification of the stages of refinement are facilitated. Refinement and implementation are controlled semantically by the satisfaction of the contracts; syntactically, a renaming is authorised. We specifically study the implementation using the Java programming language. We show how to specify classes of the Java programming language using language CO-OPN/2, so that the last stage of the process of refinement leads to a specification entirely built using CO-OPN/2 components specifying Java classes. The stage of implementation in the Java language itself is thus facilitated. The third part of this thesis shows how it is possible to practically verify that a CO-OPN/2 specification satisfies its own contract, that a stage of refinement is correctly carried out, and finally that the stage of implementation is correctly performed. These verifications are carried out using the theory of the test provided with language CO-OPN/2. Finally, the last part of this thesis illustrates the cogency of this approach by applying it to a complete and detailed case study. A distributed Java application is developped according to the method introduced for the CO-OPN/2 language. Refinement is guided mainly by the satisfaction of functional requirements and by constraints of design integrating the concept of client/server architecture. Lastly, the stages chosen in the refinement process of this development make it possible to study aspects specific to distributed applications, and to propose generic schemas for the design of such applications.