Software Engineering

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11.1 
Assess functional complexity
11.1 
Assess functional complexity
Functional analysis and allocation is performed at every level of the functional 
architecture. The initial set of functions that form the top layer of the functional hier-
archy are derived from the specified software requirements or operational model. 
FIGURE 11.1
Functional analysis and allocation tasks.

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CHAPTER 11 
Functional Analysis and Allocation Practice
These functions should represent the primary functions that the software product 
must perform. However, it may be desirable to group and organize these functions 
around a software operational concept that involves some form of initial user iden-
tification and authentication or software application initiation and presentation of 
the home graphical user interface. At this level, every function should be considered 
complex since they are at the business process or operational level of abstraction.
The complexity of every function must be assessed to determine if it necessi-
tates further decomposition to provide an uncomplicated, unambiguous functional 
depiction. Functional complexity may be recognized when any of the following 
conditions are evident:
●
  The behavior of a function requires further clarification to describe the transfor-
mation of inputs into the desired output or response.
●
  Multiple approaches to providing the functionality can be conceptualized and 
the most advantageous approach must be determined.
●
  A function involves business rules or control logic that are ambiguous or 
nebulous.
●
  A function involves accessing multiple data storage or retrieval transactions.
●
  A function involves inputs from multiple sources, such as users, external sys-
tems, or other functions.
Functions that require further decomposition are labeled functional components. 
The remainder of the functional analysis and allocation tasks should be performed to:
●
  Define the behaviors of functional components.
●
  Allocate software performance characteristics among functional components 
and units.
●
  Assess the suitability and completeness of the functional architecture.
●
  Specify the design requirements for every element of the functional architecture.
As a rule of thumb, functional analysis continues until a function is recognized of 
which the implementation is noncomplex and its behavior can be specified without 
further investigation. These noncomplex functional elements are labeled functional 
units and represent the fundamental features from which the physical architecture 
will be configured. The number of levels of decomposition will vary throughout the 
functional hierarchy due to the uneven complexity associated with a functional prob-
lem and its solution. It is not necessary to strive to have a uniform leveling through-
out the functional hierarchy. The intent is to ensure that the behavior of each function 
is well understood and that each functional unit can be unambiguously specified and 
implemented. Several guidelines apply to functional decomposition:
1. 
A function cannot be decomposed into a single function. Decomposition war-
rants the identification of at least two subfunctions.
2. 
The need for further decomposition is driven by functional complexity, and 
therefore the functional hierarchy will not be horizontally symmetrical or verti-
cally consistent in depth.

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