Model-Driven and Software Product Line Engineering - Model-Driven and Software Product Line Engineering - page 130

based on feature configurations [ARB 09]. This mechanism
can be used in conjunction with transformation languages
that provide facilities for the composition of transformation
rules. In particular, we used the oAW modeling framework
and the Xtend and Xpand model transformation languages,
which provide a mechanism based on Aspect-Oriented
Programming (AOP) for composing transformation rules (see
section 3.6.4).
Our decision models are useful to capture (1) the
relationships between features and specific transformation
rules,and(2)therequiredexecutionorderingoftransformation
rules to create products based on feature configurations. Our
basic idea to obtain a final execution scheduling is to construct
a baseline ordering, modified according to valid feature
configurations.Abaselineorderingdescribesasequenceofcalls
to base transformation rules. Our mechanism to adapt the
baseline ordering is supported by AOP concepts. We capture
in decision models information about aspects that must be
woven with a baseline ordering to adapt it. Aspects maintain
the information of what base transformation rules must be
intercepted(joinpoints)andwhatspecifictransformationrules
mustthenbeexecuted(advices)accordingtodefined conditions
on feature configurations.
Table 4.1 presents examples of conditions on feature
configurations that we can capture in our decision models.
These conditions imply modifying a baseline ordering. In the
first column, we present examples of conditions; in the second
column, we present the name of the base rule in the baseline
ordering to be intercepted (join point); in the third column, we
present the name of the specific rule (advice) to be executed if
the condition appears in a feature configuration. Thus, if the
Feature One appears Selected in a feature configuration,
regardless of the other features, Rule A must be intercepted
and the Rule A' must be executed instead. If Feature Two
appears Unselected in a feature configuration, regardless