PESTS

PESTS (Partial Evaluator of Symbolic Transition Systems) is a tool suite for the partial evaluation of finite state agents. The tool implements the algorithm for quotienting finite-state automata introduced in the paper:

Gabriele Costa, David Basin, Chiara Bodei, Pierpaolo Degano, and Letterio Galletta, `From Natural Projection to Partial Model Checking and Back’. TACAS 2018.

UPDATE: PESTS v1.2 is out with a new support for symbolic automata

Among the others, PESTS can be used to address the following problems:

1. reducing the verification of a parallel composition to that of a single component;
2. synthesizing a submodule that respects a global specification: Submodule Construction Problem (SCP);
3. synthesizing a controller for a given component: Controller Synthesis Problem (CSP).

Given a specification S and an agent A (both defined through either a deterministic finite state automaton or a symbolic automata), the tool returns (the most permissive specification of) a new agent A’ that, put in parallel with A, satisfies S.

Version

The last stable version of the tool is PESTS version 1.2 (JAR) available at https://github.com/gabriele-costa/pests/releases.

The instructions for replicating the TACAS experiments presented in

Gabriele Costa, David Basin, Chiara Bodei, Pierpaolo Degano, and Letterio Galletta, `From Natural Projection to Partial Model Checking and Back’. TACAS 2018.

refer to PESTS version 1.1 (TACAS) DOI: 10.5281/zenodo.1138898

Requirements

• Oracle Java runtime environment (JRE) or Java development kit (JDK) version 8 or greater (http://www.oracle.com/technetwork/java/javase/downloads/index.html). PESTS has been also tested with the OpenJDK version 8 (http://openjdk.java.net/)

Installation

PESTS is implemented in pure Java and requires no particular installation procedures. It is provided as a self-contained Java archive (.jar) and it can be downloaded from GitHub.

Description

The main operation performed by PESTS is the partial evaluation (aka quotienting) of a specification against a finite transition system A. The result of the partial evaluation is a new specification that another transition system B must fulfil to ensure that the parallel composition of A and B fulfils the original specification.

The inputs that must be provided to the partial evaluation procedure are:

• P: the original specification
• A: the transition system
• S: the set of synchronous actions between A and B
• G: the set of asynchronous actions of B

Usage

PESTS can be used both as a stand-alone, command line tool and a library.

PESTS as a stand-alone tool

Note: the current release of PESTS only support CLI for non-symbolic transition systems.

Open a terminal and browse to the folder containing pests.jar. Then type $ java -jar pests.jar -h to get the following help message.

$ java -jar pests.jar -h
Partial Evaluator of Simple Transition Systems (PESTS)
Usage: java -jar pests.jar INPUT [OPTIONS]

INPUT must be an existing file containing a textual description of a finite state agent

OPTIONS are a subset of the following:
-o=FILE	            write output on FILE. Writes on standard output if not specified and option -f is set to txt.
-s=FILE             read specification from FILE. Uses FALSE if not specified.
-a=v1,...,vN        use v1,...,vN as synchronous actions. Uses the empty set if not specified.
-b=v1,...,vN        use v1,...,vN as asynchronous actions. Uses the empty set if not specified.
-f=txt|svg|png|pdf  use the specified output format. Omitting this option is equivalent to -f=txt.
-v                  activate verbose output.
-h                  print this message and exit.

The INPUT file contains the transition system A, while the -s options is used to pass the (file containing the) specification P. Options -a and -b permit one to define sets S and G, respectively. Actions must be valid identifiers, i.e., alpha-numeric sequences without spaces.

Input file format

The input file contains the specification of a finite transition system defined as a deterministic finite state automaton (DFA). The file is structured in four parts:

• Initial -- specifies the name of the initial state
• Finals -- specifies the list of the names of final states
• Actions -- specifies the action labels
• Transitions -- specifies the labeled transitions of the DFA

Input file examples

The following example defines a 3-states DFA

    initial:q0;
    finals:q0,q1,q2;
    actions:a,s,t;
    q0--t->q2;
    q0--a->q1;
    q1--s->q0;

corresponding to the following diagram (where all the states are final).

          t
   +-----------> q2
   |
   |      a             
-> q0 ---------> q1
   ^             |
   |      s      |
   +-------------+

PESTS as a library

As a Java library, pests.jar must be included in the build path of the Java compiler as usual, i.e., setting the -cp option or adding it with a IDE-specific procedure.

Non-symbolic transition system. A simple and common usage scenario for deterministic finite transition systems is the following

DFAutomatonImpl P = ... // create a specification P adding states and transitions
DFAutomatonImpl A = ... // create the transition system A (similar to creating P)
Set<String> S     = ... // Set of synchronous actions
Set<String> G     = ... // Set of asynchronous actions

DFAutomatonImpl PP = Projection.unify(Projection.partialA(P, A, S, G), G);

Here the most relevant classes and methods are:

• Class it.unige.automata.impl.DFAutomatonImpl: a concrete implementation of a DFA.
• Class it.unige.automata.impl.NFAutomatonImpl: a concrete implementation of a NFA.
• Class it.unige.parteval.Projection: utility class implementing the core algorithms.
• Method partialA: the implementation of the quotienting algorithm.
• Method unify: the implementation of the unification algorithm.

Symbolic transition systems. Instead, for the partial evaluation of symbolic transition systems the common usage scenario is

EventAutomaton P = ... // create a specification P adding states and symbolic transitions
EventAutomaton A = ... // create the symbolic transition system A (similar to creating P)
Set<String> S    = ... // Set of synchronous symbolic events
Set<String> G    = ... // Set of asynchronous symbolic events
		
EventAutomaton PP = Projection.unifyS(Projection.partialS(P, A, S, G), G);

Javadoc describing the meaning and functionalities of the relevant classes are provided with the PESTS source code.

TACAS Experiments

Below we explain how to replicate the experiments presented a TACAS 2018.

TACAS virtual machine instructions

1. open a terminal and type $ java -version to check that a JRE is correctly installed and its version.
2. if no JRE is installed, install it through $ sudo apt install default-jre.

TACAS release

The TACAS release consists of a .zip archive containing:

• pests.jar: the PESTS tool binary
• test: a folder containing the files necessary to replicate the experiments presented at TACAS '18
• scp.sh and csp.sh: shell scripts to replicate the experiments

How to run the TACAS paper experiments

To replicate the experiments table presented in the paper follow the steps below.

1. Download PESTS version 1.1 TACAS (pests-v1.1-tacas.zip).
2. Decompress the .zip archive to some folder (e.g., with $ unzip pests-v1.1-tacas.zip)
3. Enter the unzipped folder and open a terminal there
4. Make sure that both scp.sh and csp.sh are executable (in case add the executable flag with $ chmod +x scp.sh and $ chmod +x scp.sh)
5. Run the shell script setting the number of experiments (between 1 and 20) to be executed. For example ./scp.sh 5 performs the first 5 experiments corresponding to the first 5 rows of the experiments table in the paper appendix (Table 4).

NOTE: For each experiment, the output of the tool has following structure.

** SCP Test number 1 **
Starting partial evaluation.
Partial evaluation: Time=10 ms, States=24, Transitions=36
Unification: Time=4 ms, States=9, Transitions=11
Writing output.
Completed.

The output shown above refers to the first line of the SCP table (** SCP Test number 1 **). The total number of states and transitions processed by the partial evaluation algorithm is reported in the third line. These values must be compared with the second and third column of the table, respectively. Instead, the total execution time is given by the sum of the two phases (i.e. partial evaluation and unification). For instance, in the example the total time amounts to 14 ms.

WARNING: Experiments above 15 may take up to some hours.

Flexible manufacturing system

The package it.unige.parteval.test includes several JUnit tests and some case studies. Moreover, the package it.unige.parteval.test.flexfact provides utility classes representing the components of the Flexible manufacturing system. These components can be used to assemble virtual plants for partial evaluation purposes.