The system catalog forms the core of your database. It comprises a set of system tables that describe all of the tables and relations contained within the database. You can have multiple system catalogs (databases), but only a single catalog may be accessed at one time. The system catalog is fully portable between machines with the same byte ordering.
AcuXDBC populates a system catalog with information it reads from your XFDs. Once this information is loaded, AcuXDBC no longer requires your XFDs. Instead, it refers to the system catalog to obtain the information needed to construct and display your COBOL tables. This gives you the option of providing end users with either XFDs for building their own system catalog or a pre-built system catalog. The ability to supply a pre-built system catalog can lead to other benefits for your applications. For example, you can also pre-build user logins, database object permissions, and complex data handling views.