This paper deals with the problem with consistency of the information model of a business system. This paper results from the methodology used in a business system's information modelling based on the idea of the two basic dimensions of the business system model. This approach combines the conceptual model with the process model. The problem with the consistency of particular models (diagrams) is discussed using the formal specification of business system modelling. Particular attention is paid to the consistency of structures: the so-called “structural consistency”, which is based on the work of M.A.Jackson.