Software Requirements Engineering

1
Software Requirements Engineering

• Ch.5
• B. Ramamurthy

2
Topics

• Requirements engineering process
• State machines
• Event-driven programming
• Table-driven methods
• Mealy Machines
• Petri nets for representing behavior of
  multiprocessors
• Use case diagrams

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.

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

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.

6
Fighter aircraft avionics
else
MA
TAK
NAV
TD
NAE
MC
LO
NAA
EE
LAN
ED
7
Finite State Machine (FSM)

• M five tuple ? S, i, T, S, d
• S set of states
• i initial state
• T terminal state (s)
• S events that bring about transitions
• d transitions
• Lets do this exercise for the avionics for
  fighter aircraft

8
State Transition table
MA LO TD MC EE ED
TAK NAV
NAV NAE LAN
NAE NAA
NAA NAE NAV
LAN
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?