1. Software Requirements Engineering
Ch.4
B. Ramamuthy
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2. Topics Requirements engineering process State machines
Event-driven programming
Table-driven methods
Mealy Machines (fig.4.4, Table 4.3)
Petri nets for representing behavior of multitasks (4.8, 4.9, Table 4.5, fig.4.10)
Context diagrams (fig 4.14)
Use case diagrams (fig 4.15)
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3. 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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4. Types of requirements
Standard scheme for realtime systems is defined by IEEE standard IEEE830.
It defines the following kind of requirements:
Functional
Non-functional
External interfaces
Performance
Logical database
Design constraints (ex: standards compliance)
Software system attributes
Reliability, availability, security, maintainability, portability
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5. 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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6. Fighter aircraft avionics
else
else
TAK MA
NAV TD
else
NAE MC
else LO
NAA EE
LAN ED
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7. 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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8. State Transition tableMA LO TD MC EE ED
TAK
NAV
NAE
LAN
NAA
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9. 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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10. Exercises 4.7 : context diagram, use case diagram 4.8 : state diagram
4.10
4.11
4.13
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