An architectural design should be the integration of knowledge and experience of all the participants in the design process. In order to make a usable model for well-integrated decision making, it is necessary to study what architects do, especially how they use constraints and images to fulfil goals and wishes of the participants. The analysis of the design process takes place with the help of the IDEF-0 technique, which is a systems-analysis technique used to structure information. The model of the process is tested by observations of design excercises. Some results of this research will be presented. The abstract mode lpresentation is translated into diagrams and drawings, which can be understood easily by everbody involved in architectural decision making.