Abstract: Software Oriented Architecture is one of the more popular and currently used architectural models. One of the essentials properties offered by this model is the loose binding between services. This property allows to indepently develop and deploy building blocks of an application. This leads to a hight mobility of the execution environment, where services can appear and disappear without a prior notivication. This paradigm brings several advantages in software designing and developpement, but there is ab big deal whis is to guaratee that applications built on top services will continue to run properly, even if the environnement is dynamic. In our work, we are interessed by one of the major problems of services communication which is services substitution. This problem is even more complex when services used are statefull. Besides, the substitution process include a look up mechanism of a compatible service, to replace the disappeared one. We work on OSGi platform and we propose an approach of services specification, in order to improve the finding of the best service for the substitution. Our contributions are then, on the first hand to provide an API based on proxies use to manage services substitutions in OSGi. On the second hand, we propose an approach of services specification based on a combined use of interface automata and CCS, to help finding the best service for the substitution.