15.1 MODEL REUSE
In many ways, the productivity of DSM can be attributed to various kinds of reuse.
Existing expert experience is used in building the modeling language, generators and
domain framework, and all of these are reused automatically each time a developer
makes a model.
Domain-Speci?¬?c Modeling: Enabling Full Code Generation, Steven Kelly and Juha-Pekka Tolvanen
Copyright # 2008 John Wiley & Sons, Inc.
397
DSM is however particularly well suited to further reuse: existing models and
model elements can be applied and referred to when making new models. Such reuse
should generally aim to be by reference, not repetition.
15.1.1 Copy by Value Versus Copy by Reference
Traditionally, there has been a distinction between two methods of copying: copy by
value and copy by reference. Although this will be familiar ground to most readers, let
us lay down some basics ?¬?rst. We will say that there is an existing element, already
used at one place in the system. The element has some content, and we want to use it in
a new place too.We will keep the details deliberately vague: element, content, place,
and system could map to many things, depending on our development process and
artifacts.
In copy by value, the content of the existing element is copied to the newplace. The
content thus exists as two separate copies, and changes to one will not affect the other.
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