Both dBASE III PLUS and dBASE IV files can be used in Visual FoxPro.
Although you can share files simultaneously between dBASE and Visual FoxPro, it is not recommended, because Visual FoxPro and dBASE have incompatible file locking mechanisms. In addition, because of the necessity of recreating index and memo field files for each application, tables are difficult to maintain.
The Visual FoxPro language is a superset of dBASE III PLUS. Your dBASE III PLUS programs can run unchanged in Visual FoxPro.
The only significant areas of incompatibility with dBASE IV are security, network functions, and the more rarely used SQL and transaction processing functions. Most SQL programs (.prs files) will need to be rewritten in Visual FoxPro. Visual FoxPro has some SQL and transaction commands with the same names as dBASE IV commands.
You can maximize compatibility by issuing the following command:
SET COMPATIBLE DB4
This command changes the way Visual FoxPro executes certain commands and functions to match the behavior of dBASE. Setting COMPATIBLE to DB4 is a great way to get your application up and running. Eventually, as you add Visual FoxPro features, you might find it easier to move away from using the compatibility feature.