Page 197 - Software and Systems Requirements Engineering in Practice

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C C h a p t e r 5 : Q u a l i t y A t t r i b u t e R e q u i r e m e n t s 163
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ADD begins by prioritizing the architectural drivers. This is done
by soliciting input from both the business and technical stakeholders.
The business stakeholders prioritize scenarios based on their business
value (High – H, Medium – M, Low – L), whereas the technical
stakeholders do so based on how difficult it would be to achieve a
given scenario during the system design, resulting in nine different
combinations in the following order of precedence: HH, HM, HL,
MH, MM, ML, LH, LM, and LL. Table 5.8 shows the prioritized
drivers for the building automation system.
From here we decompose the system by applying a series of
architectural tactics corresponding to each architectural driver.
Figure 5.7 shows the result of applying these tactics to the building
automation system. The sequence of decomposition reflects the
priority order of the quality attribute drivers in Table 5.8.
Software Management System
Software
Management Virtual FSS
System Adapter Manager
Commands Commands
Events Events
Commands
Adapter 1 … Adapter n
Events
Field Devices Commands Commands
Events Events
Field System
(a) (b)
Alarm data
Alarm
Alarms Presentation Alarm Alarms
notification Alarm notification Alarm
Events handling Events Commands notification
Commands Commands Events
Software Management System Software Management System
Virtual FSS Virtual FSS
Commands Commands Commands Commands
Events Events Events Events
Field System Field System
(c) (d)
Legend
Components Connectors
Component X Y Call-Return (X calls Y)
A B Data Access (A accesses/stores data to/from B)
Database X Y Call-Return (X accesses File-Y)
External System System Boundary
FIGURE 5.7 (a) Monolithic system, (b) support for adding new hardware,
(c) support for life-critical systems to operate within specific latency
constraints, and (d) support for internationalization