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could also become in its turn “active” and “effector”, the states through which it tran-
sits might be quantitatively different than in the case of the first response. To resolve
some of these problems, the third very useful UML type of diagram, the sequence
diagram, useful for depicting the interaction between objects in time, can come to the
rescue, like illustrated below.
anAPC :
APC
aLympN :
Lymphocite
1: recognize
2: turnActive
3: clone
aLympN-1 :
Lymphocite
4: clone
prob = p
aFirstLymp0 :
Lymphocite
5: turnMemory
6: clone
prob = 1-p
aSecondLymp0 :
Lymphocite
7: turneffector
Fig. 4.
A UML sequence diagram clarifying some of the ambiguities of the state diagram repre-
sented in fig.3. Here three more lymphocyte objects are considered, clones of the first one.
Since the publication of the “Gang of Four” Design Pattern topic [18] (classifying,
explaining and implementing 23 design patterns), the implementation of these soft-
ware OO recipes have turned out to be one of the most popular and prolific field of
today software technologies. They are not as easy to grasp as the basic principles of
OO or the basic symbols of ULM, but they are worth the learning since their imple-
mentation testifies of an accurate understanding of the problem to be handled and
equally well of the way to map it onto an OO architecture that guarantees readability,
flexibility and stability (despite this adaptability). In substance, what DP aim at is to
preserve some large space of development variability without affecting the rest of the
simulation. Some of them will be presented in the next section while describing the
minimal immune system simulation. However, the UML class diagrams discussed
before already allow introducing some simple and tricky DP. Among them, the “pro-
totype” DP has to do with the way a new object is created by cloning an existing one
(a central aspect of the diagrams above). This DP teaches you for instance not to con-
fuse a shallow copying (a T cell would be cloned without equally cloning the antigen
receptor it is composed of) with a deep copying (where the cloning of the container
implies the cloning of the content). Once a clone is born and provided many of them
are, it is important, for obvious memory reasons, to separate what can be store only
once in memory from what has to be distributed distinctively among the clones. This
is the role of the “flyweight” DP, looking for common parts in the description of
