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Software Requirements Engineering

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  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. else else else 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, 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

  8. State Transition table

  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?