The aim of this research is to realize multiple knowledge sources cooperation of problem solving in real time image processing system under parallel environment. This paper introduces a kind of expert system tool language for image understanding

V language (ver 3). The discussion of V.3 is concentrated on its knowledge representation

inference mode and control mechanism. In V.3

knowledge source is consisted of frames of typical object in image understanding

and is controlled by layered blackboard. The inference mode is mixture. Apart from these

several new ideas are also introduced. The object oriented frames present both the static knowledge (about the object) and the dynamic knowledge (methods/procedures using for image processing) at the same time. The post office may record and transmit messages between frames. Blackboard

served as control mechanism

is layered according to knowledge sources. At the end of this paper

an example

the recognition of bridge over water is discussed in detail.