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CSE298
CSE300
IOA
PRESENTATION
May 01, 1999
CSE.-IOA-1
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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
init(v1)
P1
Channel
decide(v1)
send(m(1,2))
C(1,2)
receive(m(1,2))
receive(m(2,1))
C(2,1)
send(m(2,1))
init(v2)
P2
decide(v2)
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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

<exp> :: = <simp exp> <rel op> <simp exp>

<rel op> :: =
< | >= | <= | = | >
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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.

< AUTOMATON: “Automaton” >

< TRANSITION: “Transition” >

< INPUT: “Input” >

< OUTPUT: “Output” >
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() :
{}
{
<STATES> state()(“,” state())*
(<SO> <THAT> predicate())?
}
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Translation of Grammar Cont’d

JavaCC grammar with Java code inserted to create
the IOA compiler.

states ::= ‘states’ state,+ (‘so’ ‘that’ predicate)?









void states() :
{}
{
{String lTokStr;}
<STATES> lTokStr = state()
{pwOutput.println(lTokStr);}
("," lTokStr = state()
{pwOutput.println(lTokStr);})*
( <SO> <THAT> 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(lTokStr);

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
setReady
skew
FibonacciSkew
print
Input Action
Internal Action
Output 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 (ready==true)
skew = k;
else
System.out.println(“Cannot skew: No sequence is
being generated”);
$

Public Method in Java Class
public void skew(int k) {
if (ready==true)
skew = k;
else
System.out.println(“Cannot skew: No sequence is
being generated”);
}
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Internal and Ouput Actions to Public
Methods
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
IOA Internal Action

Public Methods in Java Class
internal calculate()
pre $
return (ready);
$
eff $
current = first + second + skew;
skew = 0;
first = sec;
sec = current;
printFlag = true;
$
public boolean Precalculate() {
return (ready);
}
public void calculate() {
current = first + second + skew;
...
}
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Internal and Ouput Actions to Public
Methods
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
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.Returnflag());
}
if(askuser(“skew”))
{
ioaFibonacciSkew.skew(
inputFibonacciSkew.Returnk());
}
if(ioaFibonacciSkew.PreCalculate())
{
ioaFibonacciSkew.calculate();
}
if(ioaFibonacciSkew.Preprint())
{
ioaFibonacciSkew.print();
}
NotQuit = askuser(“cycle again”);
}
Input
Internal
Output
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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
IOA.jj
grammar
file
javacc
IOA.java
associated
Java files
ioaname.ioa
javac
MethodInfo.java
Scheduler.java
Parameter.java
*.class
java
Executable
IOA
ioaname.java
ioanameScheduler.java
paramioaname.java
ioanameScheduler
java
*.class
javac
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