DEVS Namespace for Interoperable DEVSSOA

1
DEVS Namespace for Interoperable DEVS/SOA

• Chungman Seo
• Bernard P. Zeigler
• Arizona Center for Integrative Modeling and
  Simulation
• The University of Arizona

2
Outline

• Motivation of the study
• Objectives
• Background
• Design of interoperable DEVS simulation
  environment
• Implementation of interoperable DEVS simulation
  environment
• Track Display Application
• HLA vs. SOA support for DEVS interoperability
• Conclusions
• Future work

3
The Problem

• DEVS simulators implement the DEVS modeling
  formalism in diverse programming environments,
  e.g. DEVSJAVA, ADEVS, CD, DEVSim,
  PythonDEVS
• The DEVS formalism specifies the same abstract
  simulator algorithm for any simulator
• Different simulators implement the same abstract
  simulator using different codes
• This situation
• inhibits interoperating DEVS simulators
• prevents simulation of heterogeneous models
• Each simulator can not provide platform-neutral
  message passing

4
The Need for Interoperability

• Different platforms specialize in different
  capabilities, e.g., C supports fast execution,
  but JAVA provides a better platform for web
  service development
• In our applications at JITC, ADEVS based on C
  is employed for radar track generation while
  DEVSJAVA is used for track display
• Reusability of Models increases through
  interoperability
• System of Systems (SoS) requires interoperability
  to compose new systems from existing systems
• Interoperability requires well-defined interfaces
  to use systems in different platforms or
  languages
• Web services, HLA, and CORBA provide
  communication channels between software systems
  with different platforms

5
DEVS Standardization Supports Higher Level
Web-Centric Interoperability
6
Prior Work

• Mittal and Rico developed DEVS/SOA
• it employs JAVA serialization to code messages
  into byte array
• this restricts interoperation to simulators based
  on JAVA, e.g. DEVSJAVA, and XDEVS
• It does not use DEVS namespace
• Taekyu Kim extended DEVS/SOA to run in real time
  but did not address interoperability
• Moath Jarrah developed a Negotiation Model and
  simulated it on DEVS/SOA but did not implement it
  in web services

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Objectives

• To design and implement interoperable DEVS
  Simulation environment using SOA and DEVS
  namespace
• To manage DEVS namespace for interoperable DEVS
  Simulation environment
• To implement neutral message passing between
  different DEVS simulation environments
• To show implementation of layered
  interoperability concept
• Platforms and languages neutral DEVS simulation
  environment using SOA

8
Background - DEVS Modeling and Simulation
Framework

• Set theory based system specification formalism
• Atomic model lowest level model, contains
  structural dynamics
• Coupled model composed of one or more atomic
  and / or coupled
• -gt hierarchical construction
• Basic Parallel DEVS Model
• M ltX, Y, S, dint, dext, dcon, ? tagt
• X set of input events
• Y set of output events
• S set of states
• dint internal transition function
• dext external transition function
• dcon confluent function
• ? output function
• ta time advance function
• Time base is logical time

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Background - SOA (Service-Oriented Architecture)

• Language and platform independent gt
• separation of specification and implementation
• Loosely coupled gt
• message based, synchronous and asynchronous
  interactions.
• Over the Internet gt
• No centralized control, use of established
  protocols, security considerations.
• Inter-operable gt
• Standards based.
• Transport protocol
• HTTP/HTTPS
• Data Encoding
• SOAP (Simple Object Access Protocol), XML Schema
• Interface Description
• WSDL (Web Services Description Language)
• Service Description and Discovery
• UDDI (Universal Description, Discovery and
  Integration)
• Security
• WS-Security, XML-Signature, XML-Encryption, ...

• An architectural approach to build software
  application that use services available in a
  network

Web Service
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Overall System of Interoperable DEVS Simulator
Services with DEVS namespace
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Web-enabled interoperability of DEVS components
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DEVS namespace

• Network accessible schema document
• Storage for types of messages which are used in
  DEVS models
• A unique element name in the DEVS namespace
• Register and extract domain specific schema
  through a web service
• Supports re-use, composability, and
  interoperability

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The Structure of DEVS Simulator Service

• Web Service displayed to clients

• Link between DEVS MS and
• WS operations
• Convert DEVS message to XML message

• Implement DEVS MS with various
• Languages ( Java, C, Python, Matlab)

• Manage Networking and SOAP

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The operations of DEVS simulator service
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DEVS message to XML message

• DEVS message consists of a port/value pairs
• Implementation of DEVS message is different in
  different DEVS implementations
• DEVSJAVA employs a message class for DEVS
  message
• ADEVS PortValue class is used for ADEVS message

XML message
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Track Display Application

• Shows interoperability between DEVS models in
  different implementation languages
• Consists of a TrackDisplay model and
  TrackGenerator models
• The TrackGenerators generate time indexed
  TrackData behavior
• The TrackDisplay has a capability of displaying
  track data in GUI
• Uses a message type called TrackData consisting
  of four variables
• id int xposition double yposition double
• heading double

DEVSJAVA TrackGenerator 1 Model
Coordinator
ADEVS TrackGenerator 2 Model
AXIS2 environment Apache web server
.Net environment Microsoft web server
Virtual Time Simulation
TrackDisplay for web service using AXIS2
SOAP messages
SOAP messages
SOAP messages
IP Network
17
HLA vs. SOA support for DEVS interoperability
18
Conclusions

• Designed and Implemented an interoperable DEVS
  Simulator services with DEVS namespace
• Applied to DEVSJAVA and ADEVS
• Developed the web service for handling DEVS
  namespace to provide semantic level
  interoperability between DEVS simulator services
• Implemented the platform-neutral message passing
  on the interoperable DEVS Simulation environment

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Future Work

• Design/Implement pragmatic level interoperability
• Apply interoperable DEVS simulator service to the
  other DEVS implementations (DEVS python, DEVS
  Matlab, and so on)
• Add more functions to the web service for
  handling the DEVS namespace
• Extend the platform-neutral message passing to
  support complex message types

20
Thank you
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Implement the DEVS namespace
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Example of Registration /Extraction of DEVS
message
Web Service Operation
Web Service Operation
Web Service Operation
Web Service Operation
Extraction
Registration
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DEVS simulator service for DEVSJAVA

• DEVSJAVA Modeling Simulation
• DEVSJAVA interface between operations and
  DEVSJAVA simulator
• DEVSJAVA message to XML message
• AXIS2 to generate a DEVS simulator service
• Java based web service on Apache tomcat server

• Simulator classes for virtual time and real time
  simulations
• A Atomic class contains DEVS atomic or coupled
  model using a Digraph2Atomic class
• A Digraph2Atomic class which pretends to be an
  atomic model to follow DEVS protocol during
  simulation of interoperable DEVS simulator
  services
• A XMLObjectMessageHandler class to convert
  DEVSJAVA message to XML message vice versa

DEVS Interface
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DEVS simulator service for ADEVS

• ADEVS modeling and simulation
• ADEVS interface between operations and ADEVS
  simulator
• ADEVS message converter
• .Net to generate a DEVS simulator service
• C based web service on Microsoft web server

ADEVS Library
ADEVS Interface simulator string converter of
C to VC vice versa ADEVS message converter
ADEVS Interface