Knowledge based systems are advanced systems of complex problems representation. Its architecture and representation formalisms are the base of nowadays systems. The nature of the knowledge is usually derived from the experience in specific areas and its validation requires a different methodology of the one used in the conventional systems because the symbolic characteristic of the knowledge. On the other hand, context-aware applications are designed to react to constant changes in the environment and to adapt their behavior to its users’ situation, needs and objectives. In this contribution, we describe the design, definition and evaluation process of a knowledge-based system using CommonKADS methodology in order to represent the contextual information in a formal way for Appear platform. We also validate the prototype of the context aware system in different realistic environments: an airport, an intelligent home and elderly care which is a significant step into the formally-built applications of KBS.