Service Oriented Computing allows defining applications in which components (services) can be available and selected very late during the development process or even "discovered" at execution time. In this context, it is no longer possible to describe an application as a composite entity containing all its components; we need to perform component selection all along the application life-cycle, including execution. It requires describing an application at least partially by its requirements and goals, leaving room for delaying selection; the development system, and the run-time must ensure that the current component selection satisfies, at all time, the application description. In this paper, we propose a concept of composite addressing the needs of advanced and flexible service-based applications, automating component selection and building composites satisfying the application description and enforcing minimality, completeness and consistency properties. We also propose tools and environment supporting these concepts and mechanisms in the different phases of the application life-cycle.