Abstract: In the process of product design knowledge representation, a product design process
knowledge model based on graphical semantic cognition is presented. Through the ontology semantic
analysis and the design information processing mode analysis of human brain in the process of
product design, extension origin and extension vector were presented to achieve knowledge
representation in the design process which contains growth, convergence and optimization. On the
basis of the characterization methods above, this paper studies characterization methods and
clustering mode of case library. This paper takes a machine tool appearance design as an example,
and this method has a good effect in the design process which can be a method reference for
industrial design.

Key words: graphical semantics, extenics, graphical semantic primitives, appearance design, case reasoning