1. An expert system for processing knowledge of an object system that has a plurality of elements, comprising: a) a knowledge base including a plurality of knowledge elements each of which is a framework for representing knowledge, and comprising a plurality of logical layers including: (i) a unit knowledge element descriptive layer comprising a portion of said plurality of knowledge elements each of which contains knowledge for representing a portion of a first model of the object system, said portion of the first model of the object system corresponding to each one of the plurality of elements of the object system, respectively; and (ii) a summarized knowledge element descriptive layer being hierarchically arranged above said unit knowledge element descriptive layer, and comprising a second portion of said plurality of knowledge elements each of which contains knowledge for representing a portion of a second more abstract model of the object system than said first model, said knowledge elements of said second portion corresponding to knowledge of at least one of the knowledge elements of said first portion; and b) a processor for generating knowledge from the knowledge including updated knowledge contained in the knowledge elements included in the unit knowledge element descriptive layer, to represent the second model of the object system, and storing the generated knowledge in the knowledge element included in the summarized knowledge element descriptive layer, said knowledge element in which the generated knowledge is to be stored corresponding to the knowledge element containing the updated knowledge, said updating being based on a change of status in the object system or on an explicit instruction; wherein each of said knowledge elements is a frame and each of said knowledge elements included in the unit knowledge element descriptive layer is a frame having a slot storing an output value of a sensor that observes a status value of the respective elements in the object system, and said processor performs said generating and storing in response to updating of a slot value of a frame included in the unit knowledge element descriptive layer according to a Demon process described in association with the updated slot.