Now there are several hundred relational DBMSs for both mainframe and PC environ- ments, though many are stretching the definition of the relational model. Other examples of multi-user relational DBMSs are Advantage Ingres Enterprise Relational Database from Computer Associates, and Informix from IBM. Examples of PC-based relational DBMSs are Office Access and Visual FoxPro from Microsoft, InterBase and JDataStore from Borland, and R:Base from R:Base Technologies. Relational DBMSs are referred to as second-generation DBMSs. We discuss the relational data model in Chapter 3.