Page 133 - Software and Systems Requirements Engineering in Practice

C h a p t e r 4 :
R e q u i r e m e n t s M o d e l i n g
C h a p t e r 4 : R e q u i r e m e n t s M o d e l i n g 101 101

<<include>>
Software <<include>>
Interface <<include>> Manage Logging
<<include>> and Audit Trails
<<include>>
User
Interface
Fault Security
Management Performance Management

FIGURE 4.16 Marking an area as out of scope

have a large number of diagrams. When viewing the diagrams in a
document, web document, or presentation, it is easy to get lost without
a legend. If the legend includes the diagram status, incomplete work
is much easier to find (especially if the legend information can be
queried programmatically).

Avoid the Early Use of Packages
Packages are used for partitioning work and as virtual folders to store
related artifacts. It may not be possible to discern a correct partitioning
of the model and work effort until some significant amount of use
case modeling has been completed. We have found that the premature
use of packaging may result in frequent model reorganizations. If
packaging does not follow the logical organization of the subject
matter, flaws in construction may surface at a very late date (e.g.,
components that are tightly coupled).
Do Not Substitute Packages for Abstract Use Cases
As stated previously, the model is a single unbroken directed graph.
Directed graphs or digraphs can be traversed using breadth- or
depth-first searching techniques. Substituting packages for abstract
use cases or product features breaks the graph and creates semantic
ambiguity because packages are just storage mechanisms or
placeholders; i.e., they have no meaning in the context of process
(Figure 4.17).

Every Artifact in a Model Should Be Visible on a Diagram
A model stores artifacts and their relationships. It is possible to
remove objects from diagrams without removing them from the
model. The hidden artifacts may only show up during reviews of
printed material generated from the model. In order to be able to
conduct visual inspections of the model, every artifact in it should be
visible on at least one of the appropriate types of diagram.