A Performance Evaluation of ACORN (Agent-based Community Oriented Retrieval Network) Architecture Virendra C. Bhavsar* Ali A. Ghorbani Faculty of Computer Science University of New Brunswick Fredericton, NB, E3B 5A3 Canada Steve Marsh Institute for

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A Performance Evaluation of ACORN (Agent-based
Community Oriented Retrieval Network)
ArchitectureVirendra C. BhavsarAli A.
GhorbaniFaculty of Computer ScienceUniversity
of New BrunswickFredericton, NB, E3B
5A3CanadaSteve MarshInstitute for Information
TechnologyNational Research Council, Ottawa
Canada
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Outline

• Introduction
• ACORN Multi-Agent System
• Multiple Autonomous Virtual Users
• Adaptation of ACORN for Testbed
• Experimental Results
• Future Work
• Conclusions and Future Work

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IntroductionACORN Agent-Based
Community-Oriented Retrieval Routing Network

• ACORN is a multi-agent based system for
  information diffusion and (limited) search in
  networks
• In ACORN, all pieces of information
• searches
• documents
• images, etc.
• are represented by semi-autonomous
  agents...
• Intended to allow human users to collaborate
  closely (while providing automated message
  forwarding, search, etc., but keeping user
  control)

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Degrees of Separation

• In the 1960s, Stanley Milgram showed that
  everyone in the US was personally removed from
  everyone else by at most six degrees of
  separation
• In communities, such as a research community,
  this is clear to all members
• if you want to know something, you ask someone.
• If they dont know, they may know someone else to
  ask...
• and so on
• This also works when you have something to tell
  people...
• if you want someone relevant to know, you tell
  people you know will be interested...
• and they forward the information to people they
  know will be interested..
• and so on

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Relation to Other Work

• Search Engines
• Alta Vista, Excite, Yahoo, InfoSeek, Lycos,
  etc...
• We dont aim to search the Web
• If the user has to search, its because the
  information diffusion is
• not fast enough
• not accurate enough
• Recommender Systems
• Firefly (Maes), Fab (Balabanovic)
• Content-based or Collaborative
• ACORNs agents are a radical new approach, and a
  mixture of both...
• ACORN is distributed
• ACORN levers direct human-human contact knowledge
• Matchmakers
• Yenta (Foner)
• Very close to the ACORN spirit, lacking in
  flexibility of ACORN

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Other Work, continued

• Web Page Watchers and Push Technologies
• Tierra, Marimba, Channels
• ACORN is a means of pushing new data, reducing
  the need to watch for changes
• it does not require explicit user input to
  forward information to relevant users...
• Filtering Systems
• The filtering in ACORN is implicit in what is
  recommended by humans
• If a document is judged unsuitable by a human, it
  will not be forwarded
• In addition, the owner of the document can
  control who sees it (via the migration process)
• Knowbots
• Softbots (Washington, Etzioni, Weld), Nobots
  (Stanford, Shoham)
• mobile agents for internet search
• ACORN provides diffusion also
• if search is necessary on existing information,
  these are of use
• ACORN does not (as yet) aim to search existing
  information...

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ACORN

• Using communication between agents representing
  pieces of information, ACORN automates some of
  the processes
• Anyone can create agents, and direct them to
  parties they know will be interested
• in addition, an agent carries other information,
  such as a list of owner interests (which may be
  different from the documents subject)
• The agents proceed to the suggested readers, who
  in turn can recommend others (notice this is
  human recommendation)
• In addition, agents can communicate with each
  other regarding owner interests and individual
  agent topics, and if matches are found, can
  direct each other to relevant humans (this is
  agent recommendation)
• Clearly, agent recommendation can relieve humans
  of much of the process of finding/directing
  agents to interested parties, although it may not
  be as precise

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The ACORN Mobile Agent

• represents a unit of information
• structure

Mobile Agent Name (Unique ID, timestamp) Owner
Address Dublin Core Metadata Visited Recommende
d Known
Lists of users (humans) and/or cafés the agent
has visited, is due to visit, or knows of
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The Dublin Core

• The Dublin Core is a Metadata element set, first
  developed at a workshop in Dublin, Ohio
• Includes author, title, date
• Also includes
• keywords
• publisher
• type (e.g. home page, novel, poem)
• format (of data)
• and others
• The Dublin Core presents a powerful structured
  medium for distributing human (and machine)
  readable metadata
• It also presents an interesting query formulation
  tool
• The DC home page can be found at http//purl.org
  /metadata/dublin_core

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Agent Lifecycle

• A mobile agent in ACORN (one which represents
  information) undergoes several stages in its
  lifecycle
• Creation
• Distribution
• Visiting a user
• Mingling with other agents
• Going to next site
• Return

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Creation

• Creation
• similar to creation of electronic mail messages
• other information is requested and can be
  suggested
• the system needs keywords for the
  information/query
• it also uses (as with email) a list of addresses
  to approach
• Once created, the agent is free to go on its own
  way
• migration to other sites
• approaching relevant users to distribute
  information
• and to expand list of users to approach
• mingling with other agents
• to expand the list of users to approach

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Migration

• Agent migration makes use of the ACORN Servers
  located at each site
• similar to a web server or a mail server
• each server constantly listens for communication
  from others
• Migration
• agent informs local server (where it now resides)
  of need to migrate
• local server contacts agents home server, sends
  a copy of agent core
• home server (via contact with agent owner/client)
  authorizes migration
• authorization is necessary before migration can
  be carried out
• If authorized
• home server passes back agent state copy
• local server contacts remote server (where the
  agent wishes to go)
• local server gives reference version of agent
  state to remote server
• remote server instantiates agent at its site,
  agent continues
• local server removes agent from its site

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Visiting Users

• The purpose of an agent is to distribute
  information
• To do this, it visits users and presents them
  with that information
• This process, for ease of integration with users
  workflow, is akin to mail being sent and arriving
• The users interface to ACORN (the Client) can
  filter incoming agents according to predefined
  user requirements/interests
• Users can
• file agent details
• fetch files represented by agents (if any)
• ascertain who the agent has visited (if any)
• give feedback to the agent (explicit relevance
  feedback)
• forward the agent to other users (implicit
  relevance feedback?)

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Getting User Recommendations

• Automatically
• When an agent arrives, the users Client can
  automatically
• examine the agent
• determine if it knows of any other relevant users
• these are obtained via user interaction, and from
  data gathered by agents arriving at this Client
• share that data with the agent
• send the agent on its way, retaining a copy for
  the user to examine
• Personally
• When the user examines the agent, they can
• recommend other users to visit (forward)
• recommend cafés to visit
• send the agent on its way

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The Café - Agent Recommendations

• User recommendations are not the only way an
  agent can expand its list of people to visit
• Each site can have (between zero and many) cafés
• A café is simply a meeting place for agents
• Cafés can be generic or have specific topics
  (agents can be filtered before entering)

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Cafés revisited

• In a café, at set intervals, agents present are
  compared, and relevant information exchanged
• at present, all information is public
• if you dont want to share, dont enter the café
• there is no provision for caching agent data as
  yet (so that agents can arrive, give data, and
  leave)
• this may be added at a later date
• agents reside at cafés for set lengths of time
  (currently we have a default, but intend to make
  the length of time owner selectable)
• The café represents a unique method of automating
  community based information sharing

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tom_at_ucsd.edu
ucsd.edu
ymasrour_at_ai.it.nrc.ca
ai.it.nrc.ca
S e r v e r
bob_at_ai.it.nrc.ca
dick_at_ucsd.edu
steve_at_ai.it.nrc.ca
anwhere.else
foo_at_anywhere.else
cs.stir.ac.uk
meto.gov.uk
joan_at_meto.gov.uk
Clients
jane_at_meto.gov.uk
wibble_at_cs.stir.ac.uk
graham_at_cs.stir.ac.uk
anne_at_cs.stir.ac.uk
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Security

• The system requires agent migration to other
  sites
• where there are interested parties
• At all times, the information agents are under
  the control of their owners
• Owners can deny an agents migration to another
  site, or a specific person, since agents can be
  instructed to ask their owners permission to
  migrate
• Also, we achieve persistence by having agents
  send copies of themselves back to their owners at
  each migration
• In future, we will be adding some encryption
  capability to agents

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Testing and Deployment

• A working implementation of ACORN in Suns Java
  language
• Stress testing the architecture using large
  numbers of real users - problems
• Multiple artificial users on a simulated network

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Multiple Autonomous Virtual Users

• Test-bed Several Autonomous Servers, each
  serving autonomous virtual users
• Virtual User - capable of creating agents
• - picks up a topic from
  a client cores interest
• - migrates to other
  servers
• - potential destinations

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Adaptation of ACORN

• ACORN gt100 Java classes
• Adaptation
• Removal of user interaction classes
• Removal of client behavior clases
• Removal of other extraneous classes
• Simulation of multiple client-server
  architecture run more than one server on a
  single machine
• Possibility of using multiple processor machines
• Addition of a SiteController Class

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Adaptation of ACORN (cont.)

• SiteController Class
• handles all communication between servers on a
  single machine
• resolves agent migration requests
• handles communication between different machines
• Streamer Class
• provides transport of agents across IP
• Benefits
• Removal of the need for continuous user
  interaction
• Batch mode runs
• Only 30 Java classes

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Experimental Results

• Virtual User
• two key phrases for user interests
• four key phrases about the document or search
  area
• two recommended user address in an agent
• four key phrases for specifying interests of
  each recommended user
• Porting of ACORN to many machine architectures
• O(n2) agent interactions in a Café, n - number of
  agents

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Experimental Results (cont.)
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Conclusion and Future Work

• ACORN- multi-agent system for intranet/internet
• Allows the creation and distribution of any form
  of information (images, text, etc.)
• Performance Evaluation of ACORN on single and
  multiple servers
• Novel Idea Autonomous Virtual Users
• Adaptation of ACORN
• Porting to different machines
• Further work Adaptation to Multi-processor
  machines at a single as well as multiple sites to
  exploit CANETIII