JHAV An AV Support Environment

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JHAVÉ An AV Support Environment

• Jacob Dolan
• http//www.cs.montana.edu/dolan
• Ones object is then to have a clear mental
  picture of the state of the machine at each
  moment in the computation. This object can only
  be achieved with a struggle. Alan Turing

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JHAVÉ

• What is JHAVÉ?
• How does JHAVÉ work?
• What is Web Start?

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JHAVÉ

• Java-Hosted Algorithm visualization Environment
• JHAVÉ is a support environment for developed AV
  scripting languages.
• IT IS NOT AN AV SYSTEM!

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Design Goals

• Provide visualizations that have both smooth
  flowing animations and series of discrete
  snapshots
• Provide context-sensitive textual material that
  relates to the current state of the visualized
  algorithm
• Provide input generators to create what if
  situations
• Provide methods for active participation in the
  visualized algorithm to produce stop-and-think
  situations.

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Design Motivations

• Motivations for JHAVÉ
• Availability
• Delivered via the web
• Portability
• Delivered to any platform
• Diversity
• Limited authoring language constraints
• Extendibility
• Add necessary functionality to existing AV
  systems

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Client-Server Relationship

• Client-Server Relationship
• 1. Client connects to server
• 2. Server responds with a list of available
  algorithms
• 3. Algorithm is selected by client
• 4. Server produces the visualization script,
  customizing visualization if necessary
• 5. Client renders the visualization script
• 6. If input is required, server sends input
  generator object to client, client responds with
  requested input, server generates a new
  visualization script for the client to render

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Client-Server (cont)

• Client connects to server
• Server responds with
  list, and client selects algorithm

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Client-Server (cont)

• Client customizes input if desired
• Server produces the visualization
• script and the client renders it

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Client-Server (cont)

• Input is required, so the server-client continue
  to interact

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JHAVÉ AV Engines

• JHAVÉAV Relationship
• AV system plugs into JHAVÉ
• AV system has to be written in Java and derived
  from an abstract base class called the Visualizer
  class
• AV system must output a script file of
  visualization commands. The script language can
  be defined by the individual AV system
• Because the AV system is extended by JHAVÉ it
  needs to only worry about displaying what ever
  needs rendering

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JHAVÉ AV Engines (cont)

• To become a JHAVÉ AV engine, the engine must
  declare that it is a subclass of JHAVEs abstract
  Visualizer class
• Inform JHAVÉ what capabilities it has
• Step forward, step backward, frame jumping,
  smooth animations, zooming etc.
• Implement a constructor that receives the input
  stream
• Implement getCurrentFrame, getFrameCount,
  getRenderPane
• For each ability that it declares that it has,
  the AV system must override a method declared in
  the base Visualizer class.

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JHAVÉ AV Engines (cont)

• Current AV systems that are compatible with JHAVÉ
• JSamba (smooth animations)
• AnimalScript
• GAIGS (snap shots)

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Web Start

• JRE version management
• Web Start downloads and installs the required JRE
  version for the specific application
• Web Start can manage multiple JRE versions so the
  installation does not affect already installed
  java applications

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Web Start (cont)

• Desktop Integration
• Caches applications to be available from the
  desktop, for some applications this means running
  offline
• Version Control/Updating
• Makes sure the application is up-to-date and
  download/install new versions of the application
• Security
• Runs in the sandbox

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Web Start Implementation

• Very simple implementation
• Set up a Web server
• Create a Java Networking Launching Protocol
  (JNLP) file
• Put application on Web server
• Create Web page and link to the JNLP file

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References

• JHAVÉ, http//www.jhave.org/
• Naps, Thomas L., Norton, Laura L., and Eagan,
  James R., " JHAVÉ -- An Environment to Actively
  Engage Students in Web-based Algorithm
  Visualizations," in Proceedings of the SIGCSE
  Session, ACM Meetings (Austin, Texas, March
  2000).
• Naps, Thomas L., " JHAVÉ -- Addressing the Need
  to Support Algorithm Visualization with Tools for
  Active Engagement," accepted in IEEE Computer
  Graphics and Applications, December, 2005.
• Web Start, http//java.sun.com/products/javawebsta
  rt/
• Web Start White Paper, http//java.sun.com/develop
  er/technicalArticles/WebServices/JWS_2/JWS_White_P
  aper.pdf