Software Engineering

12.1.1 
Designating structural units
Structural units are identified from the set of functional units specified by the func-
tional architecture. It is not efficient to resolve the collection of structural units as a 
one-to-one alignment with functional units. The objective of designating structural 
units is to establish a minimal but complete set of structural units from which the 

---

208
CHAPTER 12 
Configuring the Physical Architecture
software product can be configured. Structural units will ultimately be the focus of 
the initial software implementation effort to design, code, and test individual soft-
ware modules, routines, or objects. Therefore, the designation of each structural 
unit must consider the scope of functionality it is assigned, the need for interaction 
with other structural elements, and the effort necessary to achieve the integrated 
and interoperable functional performance.
The functional architecture must be evaluated to identify a set of common or 
tightly coupled functional units that may be designated a structural unit. This does 
not prohibit a single functional unit from being designated a structural unit. However, 
the challenge of this engineering practice is to organize the specified functionality in 
a practical manner that provides an efficient and effective solution. Several factors 
must be considered that affect the ability to evolve the design solution over time:
1. 
The potential for future extension or enhancement to the software functionality.
2. 
The ability to adopt or adapt to changes in the computing environment.
3. 
The ability of the software product to be modified to repair design or coding 
deficiencies.
4. 
The sequence of software integration and test activities necessary to assemble 
the software product.
Structural units should be classified by key functional categories, such as user 
interface, database transaction processing, business process function, user adminis-
tration, resource management, error handling, and data security. Criteria for identi-
fying structural units include:
●
  A single functional unit stands alone in the action it performs and there are no 
similar functional units with which it should be combined.
●
  A single functional unit is problematic, risky, or requires special engineering 
attention to warrant designating it a structural unit.
●
  A single functional unit requires significant modeling, simulation, or testing 
effort to warrant a dedicated prototyping effort and designation as a structural 
unit.
●
  Multiple functions perform similar data processing actions and can be com-
bined without increasing structural complexity or exceeding structural unit size 
guidelines.
●
  Multiple functions perform data transformation on a common data set and 
the grouping of these functions aligns well within the overall structural 
configuration.
●
  The structural complexity of the design solution will benefit from the combining 
of similar functional units regardless of the structural size guidelines.
●
  The combining of similar functional units would adversely affect software com-
ponent integration and testing.
●
  The combining of similar functional units would impact post-development soft-
ware support associated with the incorporation of changes or preplanned prod-
uct enhancements.

---