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Principles of Engineering System Design

This document discusses principles of engineering system design, focusing on graphical modeling techniques such as Functional Flow Block Diagrams (FFBD) and Petri Nets. These tools aid in visualizing and modeling the discrete-event behavior of systems, exploring dynamics triggered by specific events. FFBDs provide a hierarchical system function decomposition, while Petri Nets, introduced by Carl Adam Petri in 1962, model concurrency and synchronization in distributed systems, based on strong mathematical foundations. Real-world examples include EFTPOS systems and vending machines to illustrate these concepts.

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Principles of Engineering System Design

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  1. Principles of Engineering System Design Dr T Asokan asok@iitm.ac.in

  2. Principles of Engineering System Design GRAPHICAL MODELLING TECHNIQUES Dr T Asokan asok@iitm.ac.in

  3. BEHAVIOR MODELING Method used for exploring the dynamics of the system. Address the discrete-event behavior, which is behavior that is triggered by the occurrence of specific events. • Control, activation, and termination of system functions • Ex: FFBD ( Functional Flow Block Diagrams), Behavior diagrams, Petrinets

  4. FFBDs provide a hierarchical decomposition of the systems function and show a control structure that dictates the order in which the function can be executed at each level of the decomposition. • Series, Concurrent, selection, and multiple exit

  5. Petri Nets • First introduced by Carl Adam Petri in 1962. • A diagrammatic tool to model concurrency and synchronization in distributed systems. • Used as a visual communication aid to model the system behaviour. • Based on strong mathematical foundation. • Captures precedence relations and structural interactions of potentially concurrent and asynchronous events.

  6. t1 A Petri Net Specification ... • consists of three types of components: places (circles), transitions (rectangles) and arcs (arrows): • Places represent possible states of the system (P= p1,p2,….) • Transitions are events or actions which cause the change of state (T=t1,t2…); And • Every arc simply connects a place with a transition or a transition with a place. The state of PN is defined by the marking. p1 Asokan T ED 309 p2

  7. t1 A Change of State … • is denoted by a movement of token(s) (black dots) from place(s) to place(s); and is caused by the firing of a transition. • The firing represents an occurrence of the event or an action taken. • The firing is subject to the input conditions, denoted by token availability. Asokan T ED 309

  8. A Change of State • A transition is firable or enabled when there are sufficient tokens in its input places. • After firing, tokens will be transferred from the input places (old state) to the output places, denoting the new state. Asokan T ED 309

  9. 1 digit 1 digit 1 digit 1 digit d4 Initial d1 d2 d3 OK OK OK OK OK OK pressed Rejected! approve Reject approved Example: EFTPOS System (A Petri net) (EFTPOS= Electronic Fund Transfer Point of Sale) Asokan T ED 309

  10. EFTPOS System • Scenario 1: Normal • Enters all 4 digits and press OK. • Scenario 2: Exceptional • Enters only 3 digits and press OK. Asokan T ED 309

  11. 1 digit 1 digit 1 digit 1 digit d4 Initial d1 d2 d3 OK OK OK OK OK OK pressed Rejected! approve Reject approved Example: EFTPOS System (Token Games) Asokan T ED 309

  12. Example: Vending Machine • The machine dispenses two kinds of snack bars – Rs 20 and Rs 15. • Only two types of coins can be used – Rs 10 coins and Rs 5 coins. • The machine does not return any change. Asokan T ED 309

  13. Take Rs 15 bar Deposit 10 15 5 Deposit 5 Deposit 5 Deposit 5 Deposit 5c 0 Deposit 10 20 10 Deposit 10 Take Rs 20 bar Example: Vending Machine (A Petri net) Asokan T ED 309

  14. Example: Vending Machine (3 Scenarios) • Scenario 1: • Deposit 5, deposit 5, deposit 5, deposit 5, take Rs 20 snack bar. • Scenario 2: • Deposit 10, deposit 5, take Rs15 snack bar. • Scenario 3: • Deposit 5, deposit 10, deposit 5, take Rs20 snack bar. Asokan T ED 309

  15. Take Rs 15 bar Deposit 10 15 5 Deposit 5c Deposit 5 Deposit 5 Deposit 5 0c Deposit 10 20 10 Deposit 10 Take Rs 20 bar Example: Vending Machine (Token Games) Asokan T ED 309

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