IOA PRESENTATION

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IOAPRESENTATION

• May 01, 1999

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IOA2JAVA Tool
Joe Balthazar
Jim Byrne
Christine Kenney
Ainsley Nathaniel
Computer Science Engineering Department The
University of Connecticut 191 Auditorium Road,
Box U-155 Storrs, CT 06269-3155
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Input/Output Automata
Process
decide(v1)
send(m(1,2))
Channel
C(1,2)
receive(m(2,1))
C(2,1)
receive(m(1,2))
send(m(2,1))
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Structure of an IOA

• Main components of an I/O Automaton(A)
• sig(A), a signature
• states(A), a set of states
• start states
• trans(A), a state-transition relation that
  follows a precondition-effect style
• input actions - no preconditions and hence, are
  permanently enabled
• internal and output actions - have preconditions
  and effects
• optional tasks

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Objectives

• Create a tool to convert the general structure of
  an IOA to Java code
• IOA can be used for algorithm correctness proofs
• Recognize only a subset of the language
• Automaton name, states and data types
• Input, internal, and output actions
• Preconditions and effects
• Parses majority of language
• Convert a single IOA to a single Java class
• Produce necessary additional Java code to create
  a executable program with IOA functionality
• Code will run on one machine

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Assumptions

• Action names, parameters, and state variables are
  unique
• Deal only basic data types
• boolean
• double
• int
• Preconditions and effects written as Java Code
• May change state variables so long as same names
  are used
• Code copied directly to Java class

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Assumptions

• Internal and output actions have no parameters
• Parameters values selected by IOA code in
  preconditions based on state
• A large enough subset of IOA is not yet
  implemented to do this
• Changes to IOA code in parser
• All keywords have the first letter capitalized
  ie. Automaton, Transition, etc.
• Some symbols were changed to accommodate the
  keyboard ie. E - There exist.
• Java types were used instead of IOA types- this
  eliminated the need for a symbol table.
• Type checking done by the Java Compiler.

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Java Compiler Compiler

• Compiler Tool for Java Language.
• The Java equivalent of Lex and Yacc
• Parses grammar to produce Java code
• JavaCC uses an input file written in a standard
  BNF grammar.
• Example of simple BNF grammar
• ltexpgt ltsimp expgt ltrel opgt ltsimp expgt
• ltrel opgt lt gt lt gt

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Compiler Procedure

• Get the tokens
• The first part of the JCC specification defines
  the tokens for the language.
• Parse the Language
• The second part defines the transitions that make
  up the language.
• Generate the code
• The compiler output is generated by the insertion
  of Java code in the transitions.

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IOA Tokens

• IOA Token definitions.
• lt AUTOMATON Automaton gt
• lt TRANSITION Transition gt
• lt INPUT Input gt
• lt OUTPUT Output gt
• Resulting Java code is too complicated to put
  here, looks like assembly language.

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IOA grammar to JavaCC grammar

• IOA grammar specification translates directly
  into JCC grammar because of similarity in
  structures.
• states states state, (so that
  predicate)?
• void states()
• ltSTATESgt state()(, state())
• (ltSOgt ltTHATgt predicate())?

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Translation of Grammar Contd

• JavaCC grammar with Java code inserted to create
  the IOA compiler.
• states states state, (so that
  predicate)?
• void states()
• String lTokStr
• ltSTATESgt lTokStr state()
• pwOutput.println(lTokStr)
• ("," lTokStr state()
• pwOutput.println(lTokStr))
• ( ltSOgt ltTHATgt predicate())?

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Java file which implements the Parser

• The IOA compiler takes an automaton definition
  as input and produces an equivalent automaton,
  written in Java, as output.
• static final public void states() throws
  ParseException
• String lTokStr
• jj_consume_token(STATES)
• lTokStr state()
• System.out.println(lTo
  kStr)
• label_12
• while (true)
• if (jj_2_38(2))

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Differences in Grammars

• JCC does not permit left recursion and hence two
  transitions have to be modified.
• For example, A ? C AB is a transition with
  left-recursion.
• The equivalent transition A ? CB does not
  contain left recursion and can be used in a
  JavaCC grammar file.
• subterm subterm (opSym subterm)
• (quantifier opSym) opSym
  secondary
• (quantifier opSym)
  quantifier primary
• secondary opSym

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Left Recursion Removed

• String subterms()
• subterm() (opSym() subterm())
• String subterm()
• ( ((quantifier() opSym()) secondary())
• ((quantifier() opSym()) quantifier()
  primary())
• ( secondary() (opSym()))
• )

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The FibonacciSkew IOA

• What does it do?
• Produces the Fibonacci sequence
• The sequence can be skewed by a certain value
  from time to time
• States
• ready indicate state of sequence generation
• skew value
• printFlag indicates print state
• first, second, current holding last three
  sequence values

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The FibonacciSkew IOA

• Actions in the IOA
• Input action to start or end the sequence
• Input action to skew the sequence
• Internal action that calculates the next value in
  the sequence
• Output action that prints the next value

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The FibonacciSkew IOA
calculate
Internal Action
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IOA States to Private Data

• IOA States

automaton FibonacciSkew states ready
boolean false skew int 0
printFlag boolean false first int
1 sec int 0 current int 0

• Private Data in Java Class

class FibonacciSkew // Private Data
private boolean ready false private int
skew 0 private boolean printFlag
false private int first 1 private
int sec 0 private int current 0
// Public Methods
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Input Action to Public Method

• IOA Input Action

input setReady(flag boolean) eff if
(ready!flag) ready flag first
1 sec 0 current 0

• Public Method in Java Class

public void setReady(boolean flag) if
(ready!flag) ready flag first
1 sec 0 current 0
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Input Action to Public Method

• IOA Input Action

input skew(k int) eff if (readytrue)
skew k else System.out.println(C
annot skew No sequence is
being generated)

• Public Method in Java Class

public void skew(int k) if (readytrue)
skew k else System.out.println(Can
not skew No sequence is
being generated)
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Internal and Ouput Actions to Public Methods

• IOA Internal Action

internal calculate() pre return (ready)
eff current first second skew
skew 0 first sec sec current
printFlag true

• Public Methods in Java Class

public boolean Precalculate() return
(ready) public void calculate() current
first second skew ...
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Internal and Ouput Actions to Public Methods

• IOA Output Action

output print() pre return (printFlag)
eff System.out.println(The current
value in sequence
is current) printFlag false

• Public Methods in Java Class

public boolean Preprint() return
(printFlag) public void print()
System.out.println(The current value in
sequence is
current) printFlag false
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IOA Input Parameters

• paramFibonacciSkew.java
• Created by Parameter.java
• Simulates input parameter values for input
  actions coming in from environment
• IOA Input Action parameter

input setReady(flag boolean)

• Public Java method for each parameter

public boolean returnflag() input
getInput(flag) return retboolean(input)
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Helper Methods

• Methods for converting String to type value

private boolean retboolean(String s) return
Boolean.valueOf(s).booleanValue()

• Method to get any parameter value from user

public String getInput(String message)
String response System.out.println(Enter
message) try BufferedReader
brInp.readLine() response
brInp.readLine() catch(Exception e)
e.printStackTrace() return response
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IOA Scheduler

• FibonacciSkewScheduler.java
• Created by Scheduler.java
• Contains main program which calls a round robin
  scheduler to cycle through actions

public static void RoundRobin() boolean
NotQuit FibonacciSkew ioaFibonacciSkew new
FibonacciSkew() paramFibonacciSkew
inputFibonacciSkew new paramFibonacciSkew()
while(NotQuit) // Check each
action NotQuit askuser(cycle
again)
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Round Robin Scheduler
while(NotQuit) if(askuser(setReady))
ioaFibonacciSkew.setReady( inputFibonacciSkew.Re
turnflag()) if(askuser(skew))
ioaFibonacciSkew.skew( inputFibonacciSkew.Returnk
())
if(ioaFibonacciSkew.PreCalculate())
ioaFibonacciSkew.calculate()
if(ioaFibonacciSkew.Preprint())
ioaFibonacciSkew.print() NotQuit
askuser(cycle again)
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Future Research

• Solving Composition of Automata
• Public Composed IOA Class Approach
• All classes are in a package
• Each independent IOA class is private
• The composed IOA class is public
• IOA Class Library Approach
• All IOAs have their own class in a library
• Create a new composed IOA importing 2 or more IOA
  classes from the library
• Put back composed classes in library and reuse
• Combination of Both
• Package last composition of classes from library
• Adapt parser to handle assumes clause

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Future Research

• Generation of pre-conditions and effects in Java
• Determining parameters for internal and output
  actions
• Common mechanism for selecting values from state
• Consider distributed systems modeled by IOA
• Interaction in Java
• Use of Java distributed technologies

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References

• MIT-Theory of Distributed Systems Group
• I/O Automata Model, Language and Tool Set.
  http//theory.lcs.mit.edu/tds/vaziri/ioa.html
• S. J. Garland, N. A. Lynch, and M.Vaziri, IOA A
  Language for Specifying, Programming, and
  Validating Distributed Systems Draft, December
  1997.
• O. M. Cheiner and A. A. Shvartsman, Implementing
  An Eventually-Serializable Data Service as a
  Distributed System Building Block, July 1998.
• Java Compiler Compiler - The Java Parser
  Generator - http//www.suntest.com/JavaCC/

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Flow
javacc
javac
java
javac
java