The function relation between spatial analysis model and expert
knowledge experiences three periods. The original spatial
decision support system depends totally on models and expert
knowledge is embedded in model during the first period. In this
mode knowledge is a fixed component of model and cannot be
redesigned to adjust a changed environment (Figure 4(a)). In
the second period, more supplicated expert knowledge is
introduced and put in use under control unit in SDSS (Figure
4(b)). This mode emphasizes the importance of analysis model
and expert knowledge and they are parallel in a problem solving
in SDSS. In this way, SDSS is developed into intelligent SDSS
because expert knowledge plays a crucial role. But domain
knowledge is separately stored with model base; model
operation can be driven by the knowledge. But the middle ware,
control unit, is indispensable at this period. The third period
realizes direct communication between model and knowledge
(Figure 4(c)). This mode relates model with domain knowledge
directly and offers a mechanism for model and knowledge
interaction. Models can retrieve and use domain knowledge
according to its need and expert knowledge can retrieve and use
models. Compared with the second period, this period is a real
integration between knowledge and model. Control unit is no