"In this work an overview of the possibilities for the creation of the information models for the engineering design assembly description is proposed. Information technology models for data description are also analyzed. Special attention is paid to the engineering problem requirements. An overview of the general information structure which is the basis of the information models and the databases, is shown. Thorough investigation of the possibilities and belonging characteristics of different information models applied to engineering design, is performed. A structure of the information model for the mechanical assembly description is presented. The methods and techniques used to define the structure of the model are based on EXPRESS information technology model, accepted in 1994 as an international standard ISO 10303 - STEP, ""Product description and information exchange"". The presented algorithms enable detailed description of geometrical, topological and other relevant information about the product as well as the associated relationships. Proposed representation of the assembly can produce a structure in the form compatible to state-of-the-art commercial CAD systems."