This paper proposes a knowledge representation framework for intelligent design platform. The main objective is to develop a schema to represent the explicit as well as the implicit design knowledge, and a method to incorporate it in the design repository. The framework is based on the ontological model composed of the elements: function, behavior, structure and constraint. While structure represents the explicit knowledge of design, function, behavior and constraint incorporate the implicit ones. By an example for injection mold design case, it is shown how and to what extent major intents of a design can be represented.