The capability and functionality of SPL procedure and function programs can be used in an advantageous manner to build well-structured and maintainable programs by organizing the SPL code into subprocedures and subfunctions.
The same SPL code can be invoked multiple times from different locations within a relatively large SPL program by declaring subprocedures and subfunctions within the SPL program.
Subprocedures and subfunctions have the following characteristics:
- The syntax, structure, and functionality of subprocedures and subfunctions are practically identical to standalone procedures and functions. The major difference is the use of the keyword PROCEDURE or FUNCTION instead of CREATE PROCEDURE or CREATE FUNCTION to declare the subprogram.
- Subprocedures and subfunctions provide isolation for the identifiers (that is, variables, cursors, types, and other subprograms) declared within itself. That is, these identifiers cannot be accessed or altered from the upper parent level SPL programs or subprograms outside of the subprocedure or subfunction. This ensures that the subprocedure and subfunction results are reliable and predictable.
- The declaration section of subprocedures and subfunctions can include its own subprocedures and subfunctions. Thus, a multi-level hierarchy of subprograms can exist in the standalone program. Within the hierarchy, a subprogram can access the identifiers of upper level parent subprograms and also invoke upper level parent subprograms. However, the same access to identifiers and invocation cannot be done for lower level child subprograms in the hierarchy.
Subprocedures and subfunctions can be declared and invoked from within any of the following types of SPL programs:
- Standalone procedures and functions
- Anonymous blocks
- Procedure and function methods of an object type body
- Subprocedures and subfunctions declared within any of the preceding programs
The rules regarding subprocedure and subfunction structure and access are discussed in more detail in the next topics.