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Figure 3. Overview of the proposed approach
compute the attributes of context model element.
This is important for managing context variants as
we will see in the case study in “A Model-Driven
Framework for Managing Context-Aware Adap-
tive Service-Based Processes.”
An instance of a context model family, which
we call context product (CP), can be specified by
creating a feature configuration based on the
context feature model. Based on the feature con-
figuration, the corresponding context product is
generated automatically. The generation process,
which is model-to-model transformation, involves
evaluating the ECs and MSs with respect to the
feature configuration, removing context primitives
whose ECs evaluate to false and, possibly doing
additional processing such as removing related
context primitives.
Obviously, a particularly interesting form of
ECs is a Boolean expression over a set of variables
each of which corresponds to a feature from the
feature model. Given a feature configuration, the
value of a feature variable is true if and only if
the corresponding feature is included in the feature
configuration. In our prototype implementation
we use either Boolean expressions in Disjunctive
Normal Form (DNF), or more general XPath
expressions which can access feature attributes
and use other XPath operations, as long as the
XPath expression evaluates to a Boolean value.
The EC is represented by one or more stereotypes.
For example, the stereotype «!f1&&f2||f3» in
DNF denotes the Boolean expression
f f f
1
.
( )
.
Once created, the stereotype is available for an-
notating context primitives.
On the other hand, the ECs should be inter-
preted with respect to the OCM containment
hierarchy. In other words, if a context primitive
container is removed all the contained context
primitives are removed. For example, if entity x
is a sub-entity of the entity y, removing y requires
removing x as well.
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