This paper proposes a model for the specification and characterization of self-aware/adaptive systems. The model offers a rigorous support for the identification and management of the aspects that characterize context/self-awareness in terms of the relevant elements that determine the changes of context and the consequent related actions the system should take. These elements include the application, the architecture and the environment as perceived, also modeling the actions the system can perform to adapt to changes in the context. The proposal specifically targets the field of computing systems, however it is not limited to it. The proposed model is applied to a few self-adaptive scenarios to illustrate its potential.