Best practice for function module development

Question

When designing a function module, what is the best practice. Should we develop it so that most of the extraction is done within the function module, or should we develop it such that prior to calling the function module the extraction should be done in the main calling program and the function module would have a huge interface of many importing parameters?
For e.g. lets say for some business logic I need MATNR MTART MEINS BSTME and so on. Now by knowing the matnr I can get all the other fields. Should I create a function module with just matnr as importing parameter and do the Select on MARA in the FM or should I create the function module with all the fields as required importing parameters. What would be a best practise in such a scenario.
Thank you.

Answer 1

Now we are getting into the ecapsulation part of function groups.  Did you know that when you run your program, and it executes a FM, that ALL function modules in the function group are loaded into memory?  And that global data inside the function group can be shared across functino module calls?  This is how you would relieve your concern.  Lets say that all of your function modules belong to the same group,  And all of them need to use a record from MARA, and you don't want to do a SELECT in all of these functions.  Basically, you just create a global structure variable in the TOP include of the function group.  In the first FM, you simply do the select and put that data into the global variable, then during the next FM call(the FM must be in the same group) you can get the data from the global variable directly without having to go to the database.
Regards,
Rich Heilman