The presentation of the similarities and differences between relational modeling of data and the object oriented modeling of data is of great importance both for data base designers and for users. By being well acquainted with the relational model and by noting the similarities and differences between the two approaches to data modeling, designers will be able to turn into account and to make use of the already acquired experience as an important basis for understanding and learning the methodology of designing object oriented databases. At the time if designers know the similarities and differences between these two approaches they have the possibility to convert a relational model into an object oriented model and inversely