QUOTE : When a domain reaches a point where the knowledge for skillful professional practice cannot be acquired in a decade, more or less, then several adaptive developments are likely to occur. Specialization will usually increase (as it has, for example, in medicine), and practitioners will make increasing use of books and other external reference aids in their work.<br /><br />Architecture is a good example of a domain where much of the information a professional requires is stored in reference works, such as catalogues of available building materials, equipment, and components, and official building codes. No architect expects to keep all of this in his head or to design without frequent resort to these information sources. In fact architecture can almost be taken as a prototype for the process of design in a semantically rich task domain. The emerging design is itself incorporated in a set of external memory structures: sketches, floor plans, drawings of utility systems, and so on. At each stage in the design process, partial design reflected in these documents serves as a major stimulus suggesting to the designer what he should attend to next. This direction to new sub-goals permits in turn new information to be extracted from memory and reference sources and another step to be taken toward the development of the design.