Formal methods engineering

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Formal methods engineering

• A short overview

2
Basics

• The course was given by Hussein Zedan (Leicester,
  UK)
• over one week 30 hours
• Problem classes and assessment was done by Dragan
  Maulovic (our own associate professor)
• Problem classes in two sessions 15 hours

3
Agenda

• Part I - Rationale Why do we model?
• Part II - Finite state machines (as the assembly
  language of modeling)
• Part III Statecharts
• Part IV - Time in statecharts

4
Students background

• Should know a lot of FSMs
• Use them in
• compiler construction
• OOA/D dynamic view
• But had no idea that FSMs are assembly language
  of modeling and that they may have wider
  application areas

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Problem classes
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Coursework 1

• You are given the following vending machine
  specification The machine has one slot (for
  inserting coins) and two buttons for selecting
  the type of coffee.
• The vending machine dispenses only two sizes of
  coffee big, which costs 50p and small size
  costing 25p.
• The machine may cheat as it does not return
  change (nonetheles it gives coffee!).
• Once a coin is inserted, the customer can not get
  it back.
• After inserting the coins, the customer presses
  the coffee of choice. If the right amount of
  money was inserted, the coffee will be dispensed
  otherwise, the machine waits. Once the coffee is
  dispensed, all inserted coins are dropped in a
  money box and the machine waits for the next
  customer.
• The machine can accept 5p, 10p and 20p
  only.
• The existing machine only dispenses black coffee
  and that a customer is provided with milk cartons
  and/or portions of sugar, both free of charge.
  However, the company decided to automate these
  processes (milk and sugar) by designing a milk
  and a sugar machine! Both machines have only one
  button each that is if pressed a carton of milk
  and/or a portion of sugar will be dispensed,
  respectively.

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Coursework 2 - 1

• Give a Statechart for following informal
  specification. The objective is to specify a
  fault-tolerant solution for a computation service
  P that can be characterised as follows
• P inputs data provided by a producer on channel
  A.
• For each input x on A, a computation y f (x) is
  performed by P and delivered via channel B to a
  consumer.
• We assume a synchronous communication between
  server and environment The producer will only
  send a new job after having received a
  NEXT-message from the server computer indicating
  that P has finished the previous computation.

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Coursework 2 - 2

• Give a Statechart for a Traffic-light Controller,
  the informal description of which is as follows
• There are two sets of lights one is positioned
  over the main road (MAIN) entering the
  cross-junction, and the other is over the
  secondary road (SEC). During the daytime the
  controller operates according to one of two
  possible programs (option externally determined)
• Program A gives two minutes for the vehicles on
  MAIN, and half a minute for the vehicles on SEC,
  alternating.
• Program B gives half a minute for the vehicles in
  SEC once a signal SEC FULL goes on (the SEC
  FULL signal coming from an external sensor).

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Tools

• JFlap
• http//www.jflap.org/
• Statemate

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Feedback
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