Software Requirements
Engineering
Ch.5
B. Ramamurthy
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Topics
•
•
•
•
Requirements engineering process
State machines
Event-driven programming
Table-driven methods
•
•
Mealy Machines
Petri nets for representing behavior of
multiprocessors
Use case diagrams
•
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Requirements-Engineering
Process
• Deals with determining the goals,
functions, and constraints of systems,
and with representation of these
aspects in forms amenable to modeling
and analysis.
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Types of requirements
•
•
Standard scheme for realtime systems is
defined by IEEE standard IEEE830.
It defines the following kind of
requirements:
I. Functional
II. Non-functional
1.
2.
3.
4.
5.
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External interfaces
Performance
Logical database
Design constraints (ex: standards compliance)
Software system attributes
Reliability, availability, security, maintainability, portability
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Design methods: Finite state
machines
• Finite state automaton (FSA), finite state
machine (FSM) or state transition diagram
(STD) is a formal method used in the
specification and design of wide range of
embedded and realtime systems.
• The system in this case would be represented
by a finite number of states.
• Lets design the avionics for a fighter aircraft.
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Fighter aircraft avionics
else
TAK
else
MA
NAV
else
else
NAA
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LO
TD
NAE
MC
ED
LAN
EE
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Finite State Machine (FSM)
• M = five tuple  { S, i, T, Σ, δ }
• S = set of states
• i = initial state
• T = terminal state (s)
• Σ = events that bring about transitions
• δ = transitions
• Lets do this exercise for the avionics for
fighter aircraft
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State Transition table
MA
TAK
LO
NAA
MC
NAE
LAN
EE
ED
NAE
NAV
NAV
NAV
NAE
TD
NAA
LAN
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Lets write the embedded system
• Use the table to code a function with
case statement
• Or write a table-driven code
• Which is better and why?
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