PDS, which is designed to aid in the development of large processes, consists of three parts: Configuration Management Processor (CPIP), library system, and Process Design Language (PDL) compiler. CMP manages the outline description of the process; aids in documentation; and is the interface between user, library, and compiler. An important function is the staging of necessary or desired source code for the compiler. Only code that is affected by code changes is compiled. Since PDL is a nested scope language, this capability that enables separate compilation is essential. PDL is a language derived from Pascal. The extensions include tasking primitives; type extensions; COMMONs; array statements and expressions; improved looping, IFF, CASE, and WITH state ments; an ESCAPE statement; an ability to call foreign routines; internal routines; and the ability to restrict the use of variables of selected types to specified procedures.