Abstract: The hierarchical ontology class makes it possible to automatically construct the hierarchical model of the physical world by using the abstract mapping relationship between ontology classes with different abstraction degrees.In this paper,we redefined Ontology Class as Object based Ontology Class, and extended the definition of Flow Fragment to propose the system-centered concept of Flow-based Ontology Class. The behavior-indistinguishable flow fragment were defined. We discussed the hierarchical representation of the flow-based ontology class in two directions; the abstraction hierarchy of flow fragment and the aggregation of indistinguishable flow fragments. In the hierarchical structure, the abstraction mapping relationship between flow-based ontology classes was constructed to realize the hicrarchical modeling process based on system-centered ontology. At the same time, the hierarchical relationship of flow-based ontology classes also provides a mechanism of system-centered knowledge sharing and reuse.

Key words: Hierarchical abstraction model,Abstraction degree,Object based ontology class,Flow-based ontology class,Hierarchical structure of flow-based ontology class