Software Engineering

3.5 
 Functional architecture relationships and 
dependencies
The functional architecture describes what transactions the software product must 
carry out to satisfy the specified requirements. To determine this, the top-level func-
tions must be decomposed to identify the sequence of subfunctions, control logic 
and decision branches, and inputs and outputs necessary to enable each function. 
Functions may require computing resources, such as data storage or data transmis-
sion bandwidth, to perform effectively. The functional architecture involves the fol-
lowing relationships and dependencies with the software architecture:
1. 
Functional behavior verification (requirements baseline).
 The functional 
decomposition of the software requirements results in the definition of func-
tional behaviors that express the software response to identifiable stimulus. 
These behaviors depict functional flow timing, data flow, control flow, and 
resource utilization for each user interaction, software operation, and interface 
transaction. The accuracy and suitability of these behavioral models must be 
confirmed as a suitable interpretation of the software requirements.
2. 
Performance allocation confirmation (requirements baseline).
 The anticipated 
range of functional performance must be shown to satisfy the degree of perfor-
mance specified by the software requirements. Functional performance budgets 
should be justifiable based on the computing environment vendors’ published 
equipment characteristics.
3. 
Functional specification integrity (requirements baseline).
 The complete func-
tional architecture must be shown to address all operational or system states and 
modes of operation, user inputs, interface message profiles, and fault detection, 
isolation, and recovery solutions.

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