XMLBased Messaging in the JSIM Simulation Environment

1
XML-Based Messaging in the JSIM Simulation
Environment

• Masters Defense
• by
• Xueqin Huang

2
Acknowledgements

• Major professor
• Dr. John Miller
• Committee
• Dr. Robert Robinson
• Dr. Dan Everett
• ...

3
Overview

• Problem interoperability in federated
  simulations
• Current solution HLA
• Proposed solution Jini and XML
• Prototype implementation JSIM
• Conclusions
• Future work

4
Problem

• Reuse of and runtime interoperability b/w
  simulation components (federates) developed
  without prior knowledge of each other are the key
  issues facing federated simulation systems.

5
Current Simulation Interoperability Solution

• High Level Architecture (HLA)
• DoD mandate and IEEE standard for simulation
  interoperability
• federates interact with each other through a
  runtime infrastructure (RTI)
• all exposed simulation functionality and object
  interactions for each federate must be documented
  in its Simulation Object Model (SOM) and
  Federation Object Model (FOM) in accordance with
  the HLA Object Model Template (OMT)
• HLA-style simulation systems Federated
  Simulations Development Kit JavaGPSS

6
Problems with HLA

• RTI offers a low-level operating system like
  conceptual framework, which makes it a central
  authorization for running a federation. Pitfalls
• too complex to implement, too difficult to scale
  and evolve
• goes against the time-honored design principle of
  layering for distributed systems
• OMT is a DoD proprietary specification, which
  cannot be understood by non-HLA style systems

7
Proposed Solution with Jini and XML

• Jini the network computing model for the Java
  platform, offering
• a service-oriented peer-to-peer communication
  framework for computers of the future vs. the
  non-layered approach with HLA RTI
• a simple programming model that makes it easy to
  develop Jini-compliant distributed components vs.
  the complexity in implementing HLA RTI and
  HLA-compliant components
• XML the universal format for data exchange on
  the Web, offering
• an open standard for data exchange vs. the
  proprietary HLA OMT Data Interchange Format (DIF)
• potential syntactic and semantic interoperability
  across disparate systems vs. the limited
  interoperability with HLA

8
Jini the Network Computing Model for Java

• Offers service-oriented peer-to-peer
  communication framework for computers of the
  future
• Supports
• join/discovery protocol
• lease-based service access
• security
• distributed transaction
• object mobility
• distributed event model

9
Jini (contd)

• Participants of the Jini distributed event model
• remote event object
• event generator/publisher/source/sender
• remote event listener/subscriber/target/receiver
• also allows for third party event routing agents

1. The remote event listener registers interest
in a particular kind of event with the event
generator
Remote event listener
Event generator
Remote event
2. The event generator fires a remote event to
indicate that an event of that kind has occurred
Courtesy of Sun Microsystems
10
Data Exchange with XML

• What is XML
• self-descriptive text-based meta-data standard by
  W3C
• Sample XML document (message.xml)
• Document Type Definition (DTD) (message.dtd)
• XML Schema (message.xsd)
• XML RDF (message.rdf)
• designed for the exchange of data on the Web
• XML messaging standards
• The Simple Object Access Protocol (SOAP)
• ebXML, ...
• How XML may help with interoperability

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Data Interoperability with XML

• Syntactic interoperability
• well-defined and widely accepted format for data
  exchange
• freely and readily available standard-compliant
  tools
• Semantic interoperability
• approach 1 define a domain-specific DTD or XML
  Schema
• approach 2 use XML RDF to achieve
  ontology-based interoperability
• approach 3 use a general purpose DTD or XML
  Schema to structure the data while providing
  additional domain-specific semantic support

12
A Prototype Implementation with JSIM

• Use Jini-style publish-subscribe eventing with
  XML-based event data to leverage the power of
  mainstream interoperability technologies to
  provide an open and flexible framework for JSIM,
  a component-based simulation environment targeted
  for simulation analysts

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Publish-Subscribe Eventing in JSIM
1. Expresses interest in an event through the
publisher interface, JsimBean
Publisher
Subscriber
JsimEvent
JSIM XML message
2. Notifies the subscriber through the
JsimListener interface
Advantage It offers a simple yet powerful
communication model that allows JSIM components
to interact with each other at runtime without
prior knowledge about each other.

14
JSIM XML Messages with KOML

• KOML the Koala Object Markup Language
• the KOML serialization package provides
  bi-directional conversion b/w Java objects and
  XML
• uses a single DTD for XML data converted from all
  types of Java objects
• allows access and manipulation of the converted
  XML data at an object level instead of the
  element level
• The use of XML as the format for the exchange of
  simulation data opens up the possibility for JSIM
  to inter-operate with other simulation systems at
  both the syntactic and semantic levels.

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Enhanced Semantic Support via Performatives

• What are performatives
• meaning words that act/perform, originated from
  the speech acts theory in modern linguistics
  used in the Knowledge Query and Manipulation
  Language (KQML) to represent agent vocabularies.
• The use of performatives in JSIM messages further
  enhances the capability of JSIM components to
  dynamically make decisions based on the context
  of their conversations.

16
Architecture of JSIM
17
JSIM Events and Messages
18
Managing XML Data
19
JSIM Data That Needs to be Stored
20
JSIM Database Schema
21
Querying JSIM Database
22
Sample Query Result from JSIM Database
23
Comparison of HLA-Style Systems and Our Proposed
JSIM
24
Conclusions

• Proposed a framework for federated simulations
  that is open, flexible, extensible, and
  comparable to an HLA-style system in terms of its
  support for interoperable federated simulations.
• Laid a solid foundation for our envisioned system
  by building a prototype XML-based messaging
  simulation system in accordance with the
  framework
• Designed and implemented an easy-to-evolve
  database schema for JSIM that supports federated
  simulations

25
Future Work

• Guarantee the reliability and order of event
  delivery in JSIM using Jini event routing agents
  and event sequence number
• Explore Jinis support for distributed
  transactions to ensure all JSIM federates store
  their simulation results, or nothing is stored.
• More semantic support for the XML messages
  through XML meta-data technologies, such as XML
  RDF

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Selected Bibliography

• Abiteboul, S. Buneman, P, and Suciu, D. (2000).
  Data on the Web From Relations to
  Semi-structured Data and XML. Morgan Kaufmann
  Publishers.
• Bollinger, T. (2000). A Guide to Understanding
  Emerging Interoperability Technologies. Technical
  paper, Mitre Corporation. July 2000.
• Burret, R. (2000). XML and Databases.
  http//www.rpbourret.com/xml/XMLAndDatabases.htm.
• Finin, T., Fritzen, R., McKay, D., and McEntire,
  R. (1994). KQML as an Agent Communication
  Language. Proceedings of the Third International
  Conference on Information and Knowledge
  Management (CIKM), ACM Press, November 1994.
• Hegaret, P.L. (1999). http//www-sop.inria.fr/koal
  a/XML/serialization/.
• Kuhl, F., Weatherly, R., and Dahmann, J. Creating
  Computer Simulation System An Introduction to
  the High Level Architecture. Published by
  Prentice Hall PTR.
• Miller. J. (1999). Guest Editorial. Web-Based
  Simulation and Modeling, IEEE Potentials. Special
  Issue on Web-Based Simulation and Modeling, Vol.,
  No. (1999)
• Sun Microsystems. (2000). Jini Technology Core
  Platform Specification, v. 1.1. October, 2000.
  http//www.sun.com/jini/specs/core1_1.pdf