Information Technology Reference
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5.2.3.
The cardinality property
To fulfill the requirement
R2
presented before, which
specifies that only (maximum) one window can be automatic,
our approach includes the definition of the cardinality
property (
A
). The cardinality property is similar in form to
feature cardinality.
D
EFINITION
5.3.-
We define cardinality as a UML-like
cardinality
A =[i..j]
,where
i<=j
,
i
and
j
are natural numbers,
and
j
can be denoted by
∗
to express an unbounded number.
Cardinality (
A
) adds semantics to a constraint
C =[M,F,A, D]
by expressing the fact that the designer can create a restricted
number of bindings between model elements that conform to
M
and the feature
F
(a number between
i
and
j
).
The requirement
(R2)
is an example where cardinality is
requiredtolimitthenumberofbindingsamongmodelelements
andfeatures.Thisindicatesthatonly(amaximum)onewindow
can be automatic.
The next two subsections present the semantics of the
cardinality property in a constraint. The semantics depend
on the type of feature included in the constraint, i.e. group,
groupedorsolitary.Theintroductionofthecardinalityproperty
specifies the cardinality of the original features in the feature
model.
Cardinality on Solitary and Grouped Features.
In a
constraint
C = M, F, A = i..j],D]
where
F
is a solitary
or grouped feature, the meanings of
i
and
j
are respectively
the minimum and maximum number of model elements that
conform to
M
that can be bound to
F
. For example, if a
product line architect wants to restrict to
0
or
1
the number
of automatic windows, he must add the cardinality
A =[0..1]
to the
constraint1
presented in Figure 5.2. Thus, maximum
one window could be automatic, e.g. the
mainRoomW2
(see
Figure 5.1).
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