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

7. 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
-> hierarchical construction
Basic Parallel DEVS Model:
M = <X, Y, S, δint, δext, δcon, λ ta>
X : set of input events
Y : set of output events
S : set of states
δint : internal transition function
δext :external transition function
δcon : confluent function
λ : output function
ta : time advance function
Time base is logical time

9. Background - SOA (Service-Oriented Architecture)
Language and platform independent =>
separation of specification and implementation
Loosely coupled =>
message based, synchronous and asynchronous interactions.
Over the Internet =>
No centralized control, use of established protocols, security considerations.
Inter-operable =>
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

10. Overall System of Interoperable DEVS Simulator Services with DEVS namespace

11. Web-enabled interoperability of DEVS components

12. 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

13. The Structure of DEVS Simulator Service
Web Service displayed to clients
Link between DEVS M&S and
WS operations
Convert DEVS message to XML message
Implement DEVS M&S with various
Languages ( Java, C++, Python, Matlab)
Manage Networking and SOAP

14. The operations of DEVS simulator service

15. 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

16. 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
Coordinator
DEVSJAVA
TrackGenerator 1
Model
ADEVS
TrackGenerator 2
Model
Virtual Time
Simulation
AXIS2 environment
Apache web server
.Net environment
Microsoft web server
TrackDisplay for web service using AXIS2
SOAP
messages
SOAP
messages
SOAP
messages
IP Network

17. HLA vs. SOA support for DEVS interoperability
DEVSsimHLA
Interoperable DEVS/SOA
Platform/Language interoperability
Support
Neutral Message passing No
Middleware interoperability
Possible using a HLA bridge
Linguistic levels of interoperability
Support 2 levels (syntactic and semantic)
Support all levels (syntactic, semantic, and pragmatic)

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

19. 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

21. Implement the DEVS namespace21

22. Example of Registration /Extraction of DEVS message
Web Service Operation
Web Service Operation
Web Service Operation
Web Service Operation
Registration
Extraction 22

23. 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 23

24. 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 24