Now there are several hundred relational DBMSs for both mainframe and PC environments, though many are stretching the definition of the relational model. Other examples of multiuser 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.