In addition to inferring type relations within individual programs, we infer type relations at the system-wide level. Such relations ensure that if a variable is declared in a copybook (include file), its type is the same in all the different programs that copybook is included in. Furthermore, we infer that the types of the actual parameters of a program call at the module level (listed in the USING clause) are subtypes of the formal parameters (listed in the linkage section), and that variables read from or written to the same databases have equivalent types.