ABAP_to_the_Future

14
Shared Memory
14.2 Creating and Using Shared Memory Objects
The best way to describe how to use shar ed memory is to use an example. This
section will first present a basic example and then will present more complicated
scenarios.
In Chapter 9, you learned that objects inSAP often resemble Russian nesting dolls
in that an observer only sees the outermost doll, but inside are a series of smaller
dolls. This matches the OO principle of having each class do one thing and one
thing only.
Therefore, an application built using OO principles that uses shared memory will
have absolutely no idea th at it does in fact use sh ared memory, because it does
not need to know or care about where th e data it uses comes from. If you start
from the point of view of the human sitt ing in front of the computer or mobile
device looking at the screen and pressing buttons, you will pass through the following
layers:
왘 The outermost layer of the software is the user interface (the view), which of
course is the software from the end user’s point of view, because that’s all that
he sees. That is why ugly gray screens don’t go over so well, even if those ugly
gray screens are rendered in a web browser.
왘 The view only knows about the next layer down, which is the controller. The
controller acts as a mediator, passing user input down to the business application
(the model) and receiving back instructions from the model as to how the
state of affairs has changed in response to that user input so that the controller
can tell the view to let the user know.
왘 The model (one level down from the controller) knows about the controller it
talks to but has no further knowledge of the outside world. It is solely concerned
with business logic. That busi ness logic almost always needs to access
information from the database, but the model does not know or care if the
information is actually coming from the database or an external system or from
the Planet Bong in the Constellation ofHorseradish Sauce. The model delegates
the task of getting the data it needs to yet another class, whose sole task is to
retrieve data.
왘 The next layer is the persistency layer, and usually the clas s that performs this
layer’s function simply performs a big bunch of database reads in its various
methods. It could of course use RFC call s to other systems or call SAP Process
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