An Object Exchange Model Template For Distributed Simulation

1
An Object Exchange Model Template For
Distributed Simulation

• Gary Tan, Na Zhao,
• National University of Singapore
• Simon Taylor,
• Brunel University, UK

2
Scope of Presentation

• Project Aim and Methodology
• Generic Runtime Infrastructure for Distributed
  Systems (GRIDS)
• Message-passing vs. Object-passing
• Object Exchange Model Template (OEMT)
• Case Study
• Discussion and Proposed Improvements on OEMT
• Conclusion and Future Work

3
Scope of Presentation

• Project Aim and Methodology
• Generic Runtime Infrastructure for Distributed
  Systems (GRIDS)
• Message-passing vs. Object-passing
• Object Exchange Model Template (OEMT)
• Case Study
• Discussion and Proposed Improvements on OEMT
• Conclusion and Future Work

4
Project Aim and Methodology

• The aim of this research is to investigate and
  critically evaluate the capability of the OEMT to
  standardize object exchange model in distributed
  simulation.

• The outline of the flow of research is presented
  as following
• Background Research and Problem Specification to
  identify the significance of object passing in
  distributed simulation and specify the object
  standardization problem.
• Practical Research to examine critically the
  capability of OEMT to standardize object exchange
  model by case study.
• Experience Gained to improve the OEMT into a
  more robust one based on case study experience.

5
Scope of Presentation

• Project Aim and Methodology
• Generic Runtime Infrastructure for Distributed
  Systems (GRIDS)
• Message-passing vs. Object-passing
• Object Exchange Model Template (OEMT)
• Case Study
• Discussion and Proposed Improvements on OEMT
• Conclusion and Future Work

6
What is GRIDS?

• Generic Runtime Infrastructure for Distributed
  Simulation
• Middleware Architecture to overcome
  incompatibilities of various simulation products
  and responsible for the communication between
  individual simulations.

7
Major Elements of GRIDS

• Boot Server
• Client
• Thin Agent
• Metadatabase

8
Technical Details of GRIDS

• Peer-to-peer communication.
• Lightweight middleware architecture.
• Provides 4 basic sets of services to each
  simulation Communications, Simulation Interface,
  Data services and Thin Agent services.
• Extra services extensible through the use of
  thin agents.

9
Scope of Presentation

• Project Aim and Methodology
• Generic Runtime Infrastructure for Distributed
  Systems (GRIDS)
• Message-passing vs. Object-passing
• Object Exchange Model Template (OEMT)
• Case Study
• Discussion and Proposed Improvements on OEMT
• Conclusion and Future Work

10
Object-passing vs. Message-passing

• Real-life instances of object/entity exchange
• Advantages of employing object-passing mechanism
  in addition to traditional message-passing in
  Distributed Simulation
• It is easier to keep the details of the object
  and to establish a standard whereby objects can
  be recognized uniquely.
• Object-passing allows the provision of methods
  that the receiving federates may invoke to
  extract information from the object.
• Standardization of object

11
Scope of Presentation

• Project Aim and Methodology
• Generic Runtime Infrastructure for Distributed
  Systems (GRIDS)
• Message-passing vs. Object-passing
• Object Exchange Model Template (OEMT)
• Case Study
• Discussion and Proposed Improvements on OEMT
• Conclusion and Future Work

12
Object Exchange Model Template (OEMT)
The GRIDS Object Exchange Model Template defines
the format and syntax for recording information
in GRIDS Distributed Simulation object models, as
well as mandatory specific data that defines each
model uniquely from others.

• Provides a template to facilitate a standard
  understanding of objects passed between
  simulations.
• Uses XML as the standard for recording the
  attributes and methods of an object.

13
OEMT Original Components

• Name of Model
• Model Description Link
• Technical Details
• Object attribute specification
• Object method specification
• General Details of each Implemented Object

14
Scope of Presentation

• Project Aim and Methodology
• Generic Runtime Infrastructure for Distributed
  Systems (GRIDS)
• Message-passing vs. Object-passing
• Object Exchange Model Template (OEMT)
• Case Study
• Discussion and Proposed Improvements on OEMT
• Conclusion and Future Work

15
Case Study Singapore Mass Rapid Transit (MRT)
System Simulation

• This case study is a distributed simulation
  instance of transportation system which
  investigates the flow of passengers and trains on
  the Singapore MRT system and its relationship
  with the safe capacity of a MRT station.

Figure MRT System Conception Model
16
MRT Station Object Exchange Relationship
17
Integrate Simulation Model with GRIDS Client
18
Object Specification Using OEMT

• Train objects represent the entities transferred
  between the federates. It carries information
  such as trainID, capacity, total passenger
  number, number of passengers to each station,
  etc.
• The GRIDS OEMT is employed to specify the train
  object. The template has a certain set of
  information to be filled in. The basic methods
  and variables are made known in this template, so
  that other federates can access appropriately.

19
Table 1 Exchange Object Information
20
Table 2 Exchange Object Attributes Table
21
Table 3 Exchange Object Methods Table
22
Table 4 General Details of Exchange Object
23
Train Object Implementation

• Attribute Field
• Method Field

24
Attribute Field of the Train Object ---
Attribute Information File (AIF)
25
Attribute Field of the Train Object ---
Document Object Model Tree
26
Method Field of Train Object
Method example
27
Method Invocation and Result

• setAttrValueInt(capacity,500)
• setAttrValueInt(totalpsgnum,300)
• setAttrValueInt(psgnum_to_EW1,50)

28
Scope of Presentation

• Project Aim and Methodology
• Generic Runtime Infrastructure for Distributed
  Systems (GRIDS)
• Message-passing vs. Object-passing
• Object Exchange Model Template (OEMT)
• Case Study
• Discussion and Proposed Improvements on OEMT
• Conclusion and Future Work

29
Discussion and Proposed Improvements on OEMT

• OEMT Components Evolvement
• Name of Parent Object catering to the
  inheritance characteristic of object-oriented
  programming, to record the name of parent object
  of the current model.
• Names of Children Objects to record the names of
  children objects of the current model.
• Time Representation to specify the timestamp and
  lookahead of the instances of the object.
• Attribute Field Format Representation to specify
  the data structure of object attributes used in
  object model implementation.

30
Scope of Presentation

• Project Aim and Methodology
• Generic Runtime Infrastructure for Distributed
  Systems (GRIDS)
• Message-passing vs. Object-passing
• Object Exchange Model Template (OEMT)
• Case Study
• Discussion and Proposed Improvements on OEMT
• Conclusion and Future Work

31
Conclusion

• OEMT is a efficient tool to standardize object
  exchange model
• It provides a commonly understood mechanism and
  general coordination among members of a
  federation.
• It provides Mandatory Object Methods Table to
  describe the methods to access the content of the
  object.
• It separates the manipulation of exchange object
  from simulation models. Therefore facilitate the
  design and reuse of common tool sets for
  development of distributed simulation object
  models.

32
Conclusion (cont.)

• It provides the GRIDS Boot Server a standard to
  distribute object information to the DDM Thin
  Agents of the various federates.
• The improvement provide a more robust and more
  advanced OEMT

33
Future Work

• much OEMT work remains to be accomplished
• Develop online Object Exchange Model Repository
  (OEMR) and Application Tools
• Make OEMT an International Standard

34

• End of Presentation