Page 123 - Software and Systems Requirements Engineering in Practice

92 S o f t w a r e & S y s t e m s R e q u i r e m e n t s E n g i n e e r i n g : I n P r a c t i c e

Ideally, the feature tree would be supported in the modeling tool
being used. If not, any graphical media could be used to illustrate the
full scope of features in the idealized product. Of course, not all the
features identified would make it into the final product; they would
need to be prioritized. After an analysis effort to expand the product
features into well-defined, testable requirements, a product release
would then be specified with the desired features. During initial
product definition, a feature model is kept relatively “lightweight.”
However, the same model can be extended to fully support a product
line. It can also be used to define product variations or customization
that may be made by the user after delivery. Feature models are
especially useful in identifying test cases where the system can be
configured by the user after delivery.

Analyzing Product Features and Creating a Use Case Model
Once we have a draft set of features, we are able to start creating a
model from which we will derive all our customer requirements (all
of them, before ranking). Product features become high-level abstract
use cases, from which we start the decomposition process to elicit
details that will become requirements (Figure 4.9). As we go through
each of the features, scenarios are created describing the feature in
action; the scenario diagrams describe the usage details (Figure 4.10),
and the use case diagrams provide structural information; e.g., which
other use cases (or processes) are included or sometimes included
(called extending use cases).

Delete Event
Creation Date:2/26/2006
Modification Date:1/15/2007
Modified By:RDM
Status:Preliminary

<<extend>>
Official
Delete event Delete event
interface
<<include>>
<<include>> Delete event from
<<include>> competitor calendar
Delete event from
team calendar Delete event from
event calendar
Delete event record from
results database

FIGURE 4.9 Use case decomposition