This paper presents an overview of frame–based knowledge representation and Structural Modelling approach as well as a new extension of frame–based knowledge representation schema is described. The extension of schema is a result of analysis of student works and it can be used in Structural Modelling approach to improve knowledge acquisition and representation about systems. Three differently structured system models are given to show the possible knowledge representation forms that are found in student works. The created schema extension can be implemented in the already developed frame–based knowledge representation tool, which purpose is to support Structural Modelling approach.