An upper abstraction layer for ?Reasoning? on CAAD tools ? Two interfaces

New inventions and changes in technology and methodologies affect design activity frequently resulting in unpredictable effects on the final design solution, hence on the real outcome - unsatisfactory buildings. To avoid these consequences, it is necessary to store and exploit ever-growing knowledge and experiences that allow these problems to be overcome. An innovative `Abstraction Layer´ overlying existing application programs has been introduced to model a Reasoner that verifies the coherence of design solutions. This one has been developed by means of an entity class based on ontologies at semantic level, not data. This paper explains how the Reasoner prototype is linked with usual CAAD and BIM tools in order to demonstrate the insight. This research is mainly related with architectural and construction design - but can also be applied to many sectors.