Page 132 - Software and Systems Requirements Engineering in Practice

100 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

objects, and boundaries or interfaces are the nodes, and the
relationships between them are the vertices. However, in order to
keep the model simple enough to analyze programmatically, the core
of the graph will be the relationship between the use cases and
product features. This heuristic, along with the heuristics that describe
the use of factors and boundaries, provides one of the semantics for
model completion.
The Early Modeling Effort Should Cover
the Entire Breadth of the Domain
“Drilling down” too soon risks missing interfaces and subject areas that
need to be modeled. By modeling across the entire domain, identifying
major areas to be modeled and those that are out of scope, missing
interfaces will become readily apparent. For example, in the event
management system for the Olympics, rather than the context diagram
showing just event management, the first one or two high-level
diagrams should include information on team management, competitor
management, etc. Once the interfaces between these functions have
been identified, then modeling of the event scheduling domain can
proceed with confidence that all interfaces to outside organizations,
people, and systems have been identified (see Figure 4.15).

Identify “Out-of-Scope” Use Cases as Early as Possible
Define scope and identify “out-of-scope” domains as quickly as
possible. We suggest color-coding high-level use cases that are out of
scope (see Figure 4.16). When working with distributed teams, it is
most important to identify out-of-scope subject areas, to avoid
wasting time on material not relevant to the project.

Every Diagram Should Have an Associated
Description and Status
Ideally the status will be in a legend on the diagram (see the engineering
drawing example shown in Figure 4.1). Real-world models tend to

The Olympics Scheduling System

<<include>> <<include>>
<<include>>

Event Management Competitor Management

Team Management

FIGURE 4.15 Initial modeling effort is cross-domain