Architectural design is a purpose-oriented collective process defined in time, split up into phases, carried out directly or indirectly by numerous professional profiles and characterized by the co-presence of numerous disciplines and specialist skills. The efficiency of a shared design among multiple designers depends on how much the actoris semantics of the used terms are interpreted correctly by all the other actors involved in the design process without misunderstandings. The chosen way to find an answer to these questions is the development of a Collaborative Architectural Design system based on Knowledge formalized by Ontologies. An ontology has been implemented using three different approaches to define an entity based on Lisp, Protégé and Altova.