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Gedistribueerde AI: Overview

Gedistribueerde AI: Overview. Concurrency - Communicating Sequential Processes - Concurrent Constraint Programming Agent-Oriented Programming - 3APL. Evolution. Mastering Complexity : From Operating Systems (mutual exclusion, scheduling) To Global Computing

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Gedistribueerde AI: Overview

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  1. Gedistribueerde AI: Overview • Concurrency - Communicating Sequential Processes - Concurrent Constraint Programming • Agent-Oriented Programming - 3APL

  2. Evolution Mastering Complexity: From Operating Systems (mutual exclusion, scheduling) To Global Computing Bioinformatics Multi-Agent Systems (negotiation, human interactions)

  3. Abstraction Procedures  Classes (Objects)  Agents (Subjects)

  4. Concurrency Main Features • Communication • Coordination • Real-Time • Non-determinism • Deadlock • Livelock

  5. Founding Fathers • E.W. Dijkstra: - Guarded Command Language - Weakest Precondition Calculus - Semaphores (Mutual Exclusion) • T. Hoare - Hoare Logic - Communicating Sequential Processes (CSP) - Monitors • R. Milner - Calculus of Commincating Systems (CCS) - PI-calculus (mobility) • V. Saraswatt - Concurrent Constraint Programming (CCP)

  6. CSP Process consists of • Internal Computation • Interface - Static (Signature) - Dynamic (Behavior)

  7. A Coffee Machine Events: coffee, thee A machine with buttons (menu) coffee thee

  8. Interfaces in OO Class Stack push pop Events: push(v), pop(v) Behavior: ?

  9. Operational Semantics  Labeled Transitions: P  Q • P,Q: Processes •   =a,b,c,.. , - a,b,c,..: External Events - : Termination - : Internal action

  10. Computation 1 2 3 P1  P2  P2  … • Finite • - successfull termination • - deadlock • Infinite • - fairness (strong, weak)

  11. The STOP-Process The process models inaction STOP STOP

  12. Performing Events a P Event Prefixing: Intuitive meaning: do firstathen P Formally (a P)  P a

  13. A Light Bulb on (on (off  stop))  (off  stop) off on (off  stop)  stop off

  14. Finite Automata P1 on P0 off stop P1 = on (off  stop)) P1=(off  stop)

  15. Making Choices(what’s life all about, isn’t it?) Choice Construct Meaning choose aA and continue with P(a) Formally x: A  P(x) (with A) (x:AP)  P(a) for aA a

  16. Example x : coffee,chocolate  P(x) P(coffee) = x : milk,black  stop P(chocolate) = x : hot, cold  stop

  17. Example (Cont’d) coffee (x : coffee,chocolate  P(x)) (x : milk,black  stop) stop milk

  18. Example (Cont’d) P0 chocolate P2 coffee hot cold milk P1 stop black

  19. Compound Events Communication Events C.V C: Channel V: Value syntax behavior C!V  P C.V (C!V  P) P output C?x P(x) C.V (C?x P(x)) P(V) input

  20. Example: A Simple Filter in?x out!op(x)  stop in op out

  21. Unix-Shell Scripts ECHO ! “please enter your name”  READ ? name  ECHO ! “welcome name”  stop

  22. Recursion N=P N: name P: process Example: light = on(off  light)  P Q N=P  N Q

  23. The Light Bulb (again) on (on (off  light)) (off  light) on (off  light) light on light P off

  24. The Dining Philospher P=think leftforkrightfork eatP

  25. Cognitive Robotics Sense-Act Cycle Cycle= x: Events  Act(x) Act(x) = a(x) Cycle

  26. Deriving Transitions Proof Rules 1 1 P1 Q1 … Pn Qn  P Q

  27. Mutual Recursion Example LIGHT=on ON ON=off  LIGHT

  28. Counter Example inc dec count(0) = inc  count(1) count(n+1) = x:{inc,dec}  P(x) P(inc) = count(n+2) P(dec) = count(n)

  29. Computation Graph inc inc inc count(0) count(1) count(2) count(3) … dec dec dec

  30. External Choice Syntax Semantics P  Q a P  P'  P  P' a P  Q P'  Q P  Q  P'

  31. Fifo Buffer in buffer out B() = in?x  B(<x>) B(<v>.s) = in?x  B(<x,v>.s)  out!v  B(s)

  32. Internal Choice Syntax Semantics P  Q P  Q P 

  33. Tossing a Coin Toss = (head Toss)  (tail Toss )  toss P head tail  Q

  34. Termination SKIP The process indicates successful termination: SKIP STOP 

  35. Sequential Composition Syntax Semantics P;Q  P  P'  P  P'   P ; Q  P';Q P ; Q  Q

  36. Purchase Purchase=Choose;Pay Select= select  (SKIP  return  Select) Pay= cash  receipt  SKIP  card  swipe  (receipt  sign  SKIP  reject  Pay)

  37. A One-Time Stack A Finite Representation Push = in?x  (Push; (out!xSKIP))  pop SKIP

  38. A Computation in.5 Push Push; (out!5 SKIP) Push;(out!3SKIP); (out!5 SKIP) SKIP;(out!3SKIP); (out!5 SKIP) (out!3SKIP); (out!5 SKIP) SKIP; (out!5 SKIP) out!5 SKIP SKIP in.3 pop  out.3  out.5 

  39. Concurrency Communication: Message Receiver Sender • Synchronous • Asynchronous • Broadcast

  40. Rendez-Vous parameters Callee Caller synchronization suspended method result

  41. Parallel Composition • Interleaving • Synchronization on common actions P | Q

  42. Architecture b a c P Q b b Interface(P) = {a,b} Interface(Q) = {b,c}

  43. Semantics Interleaving Synchronization  P  P'  P || Q  P' || Q   P  P' P  Q'  P || Q  P' || Q '

  44. A Skating Race Syntax A Run start  finish1  STOP || start  finish2  STOP start start  finish1  STOP || start  finish2  STOP finish1 finish1  STOP || finish2  STOP finish2 STOP || finish2  STOP STOP || STOP

  45. Modeling a False Start Pi= start  finish1  STOP + starti Pi

  46. Interleaving Syntax Semantics P ||| Q  P  P'  P ||| Q  P' ||| Q

  47. The Counter Example Revisited Count= inc  (dec  STOP) ||| Count) dec STOP dec  STOP dec (dec  STOP) ||| Count STOP ||| Count

  48. Dynamic Process Creation inc Count (dec  STOP) ||| Count (dec  STOP) ||| (dec  STOP) ||| Count inc

  49. A Bag Syntax A computation step Bag Bag = in?x  (out!x  STOP) ||| Bag) in.3 (out!3  STOP) ||| Bag)

  50. Buffers P= c?x  d!x  P Q= d?x  e!x Q One-place Buffers A Pipeline Synchronization on events: P || Q d.v

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