An SQL catalog consists of a set of tables and views which describe tables, views, indexes, packages, procedures, functions, files, sequences, triggers, and constraints.
This information is contained in a set of cross-reference tables in libraries QSYS and QSYS2. In each SQL schema there is a set of views built over the catalog tables that contains information about the tables, views, indexes, packages, files, and constraints in the schema.
A catalog is automatically created when you create a schema. You cannot drop or explicitly change the catalog.