The signature can be thought of like a ‘format-level identifier’ of a file. When a file’s format-level ID changes, you have to recompile programs that use the file or be prepared for a “format level check” error. The format of the file has changed in a way that makes it incompatible with previous versions.

When a service program signature changes, it’s a signal to your programs that the service program has become incompatible. You need to re-bind your programs in that case. You probably also first need to recompile your programs since a new signature indicates changes to parameter definitions.

If you used binding language to control signatures and you changed the service program in a way that allowed the old signature to remain valid while adding a new signature, then you don’t need to do anything to your old programs. Any new programs that needed the new interface would be created over the new signature. Any old programs that you wanted to use the new signature would probably have coding changes and be recompiled.

In short, if you are only changing the internals of a service program, your external programs should be fine. But if you are changing the interfaces between the programs and the service program, then recompiling needs to be done since the programs have coding changes anyway. The interfaces include the sequence of the procedures that are exported.

Tom