The enclave defines the scope and visibility of the following types of data

Automatic data: Automatic data is allocated with the same value on entry and reentry into a routine if it has been initialized to that value in the semantics of the language used, for example, data declared using the PL/I INIT() option. Values of the data at exit from the routine are not retained for the next entry into the routine. The scope of automatic data is a routine invocation within an enclave.
External data: External data persists over the lifetime of an enclave and retains last-used values whenever a routine is reentered. The scope of external data is that of the enclosing enclave; all routines invoked within the enclave recognize the external data. Examples are C or C++ data objects of extern storage class, COBOL data items defined with the EXTERNAL attribute, Fortran common blocks, and PL/I data declared as EXTERNAL.
Local data: The scope of local data is that of the enclosing enclave; however, local data is recognized only by the routine that defines it. Examples are any C or PL/I variable with block scope, any Fortran data declared as AUTOMATIC, and any non-EXTERNAL data item in COBOL.