Agent Platforms etc

1
Agent Platforms etc

• Martin Beer,
• School of Computing Management Sciences,
• Sheffield Hallam University, Sheffield,
• United Kingdom
• m.beer_at_shu.ac.uk

2
Overview

• Computational organization theories
• Organizational dimensions
• Agent platforms
• JADE and FIPA
• FIPA Specifications
• The JADE Platform
• Jade In Action - Demo

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MAS organizational dimensions

• (a) Structure
• Centralized versus decentralized
• Flat versus hierarchical

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4
Cooperative
Self-interested
Group
Team
Hierarchy
Market
Federation
Community of practice
Coalition
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• (b) Dynamics
• Coupling/relationships and roles
• Fixed coupling
• Variable coupling
• Evolutionary coupling
• (c) Degree of specialization and of redundancy
• Non-redundant, specialized organization
• - every agent Ai knows to carry out task Ti
• Non-redundant, generalist organization
• - every agent Ai knows to carry out tasks
  T1i..Tmii
• Redundant, specialized organization
• - group of agents Gai know to carry out task Ti
• Redundant, generalist organization
• - group of agents Gai know to carry out tasks
  Ti1...Tim

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Agent platforms

• Solve problems using agent and MAS technology
• Analysis
• Design
• Implementation
• Test
• Maintenance
• Methodologies
• Agent-oriented software engineering (see next
  class)
• MAS platforms and languages

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• Agents must have a support for the tasks they are
  required to do
• distributed execution
• communication
• sense the environment

Environment
Agent application (Client)
Agent platforms
Middleware
Other agent applications
Operation system
Transport layer
Network
Fat client thin middleware vs Thin client fat
middeware
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• FIPA Abstract Architecture specifications deal
  with the abstract entities that are required to
  build agent services and an agent environment
• Specifications
• Abstract Architecture - focus on
  interoperability
• Domains and Policies - enforce constraints on
  the behavior of agents within agent
  environments - encoding - non-local access -
  QoS (encryption, non-repudiation) - number of
  agents - system resources

(source 1)
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Directory entry for ABC Agent-name
ABC Locator Transport-type Transport-specific-ad
dress Transport-specific-property HTTP http//ww
w.whiz.net/abc (none) SMTP Abc_at_lowcal.whiz.net (
none) Agent-attributes Attrib-1 yes
Attrib-2 yellow Language French, German,
English Preferred negotiation contract-net
(source 1)
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(source 1)

• FIPA Agent Communication specifications deal
  with Agent Communication
• Specifications
• ACL Message Structure - specifies the elements
  of the FIPA-ACL messagethe elements are -
  performative - sender, receiver, reply-to
• - content
• - language, encoding, ontology
• - protocol, conversation-id, reply-with,
  in-reply-to, reply-by

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(source 1)

• FIPA Interaction Protocols (IPs) specifications
  deal with pre-agreed message exchange protocols
  for ACL messages. A FIPA ACL-compliant agent need
  not implement any of the standard IPs, nor is it
  restricted from using other IP names. However, if
  one of the standard IP names is used, the agent
  must behave consistently with the IP
  specification given here.
• Specifications
• Interaction Protocol Library
• Request Interaction Protocol
• Query Interaction Protocol
• Contract Net Interaction Protocol
• Iterated Contract Net Interaction Protocol
• English Auction Interaction Protocol
• Dutch Auction Interaction Protocol
• Brokering Interaction Protocol
• Recruiting Interaction Protocol
• Propose Interaction Protocol

Interaction Protocols (1/3)
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Interaction Protocols(2/3)
(source 1)
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Interaction Protocols(3/3)
(source 1)
(source 1)
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(source 1)

• FIPA Communicative Act (CA) specifications deal
  with different utterances for ACL messages.
• Specifications
• Communicative Act Library
• FIPA Communicative Acts
• Accept Proposal Agree Cancel Call for Proposal
• Confirm Disconfirm Failure Inform
• Inform If Inform Ref Not Understood Propagate
• Propose Proxy Query If Query Ref
• Refuse Reject Proposal Request Request When
• Request Whenever Subscribe

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(source 1)

• FIPA Content Language (CL) specifications deal
  with different representations of the content of
  ACL messages.
• Specifications
• Content Language Specification
• FIPA-SL (Semantic Language) Content Language
• - a general purpose representation
  formalism that may be suitable for use in a
  number of different agent domains
• FIPA-CCL (Constraint Choice Language) Content
  Language
• - intended to enable agent communication for
  applications that involve exchanges
• about multiple interrelated choices.
• - based on the representation of choice
  problems as Constraint Satisfaction Problems
  (CSPs)
• FIPA-KIF (Knowledge Interchange Format) Content
  Language
• - goal - to specify KIF as a language
  for use in the interchange of knowledge among
  disparate computer systems (created by
  different programmers, at different times, in
  different languages...)
• FIPA-RDF (Resource Description Framework)
  Content Language
• - RDF framework is based on an
  entity-relationship model proposes XML as
  encoding syntax
• - FIPA-RDF deals with how objects,
  propositions and functions can be expressed in RDF

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• Content "(" ContentExpression ")".
• ContentExpression IdentifyingExpression
• ActionExpression
• Proposition.
• Proposition Wff.
• Wff AtomicFormula
• "(" UnaryLogicalOp Wff ")"
• "(" BinaryLogicalOp Wff Wff ")"
• "(" Quantifier Variable Wff ")"
• "(" ModalOp Agent Wff ")"
• "(" ActionOp ActionExpression ")"
• "(" ActionOp ActionExpression Wff ")".
• Quantifier "forall "exists
• ModalOp "B "U "PG "I".
• ActionOp "feasible "done".
• IdentifyingExpression "(" ReferentialOperator
  Term Wff ")".

FIPA SL
not in SL0
not in SL2
not in SL1
not in SL0, SL1, SL2
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(source 1)

• FIPA Agent Management specifications deal with
  the control and management of agents within and
  across agent platforms.
• Specifications
• Agent Management
• Agent Support for Mobility

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Agent Management

• Directory Facilitator (DF)
• provides a yellow pages directory service to
  agents
• an AP can have more than one DF
• Operations that DF must support register,
  deregister, modify, search
• Agent Management System (AMS) - management of
  the AP
• only one AMS per AP
• maintains and controls agent life-cycle
• authorization for agents to access MTS
• operations that AMS must support register,
  deregister, modify, search,
  get-description
• can instruct the AP to suspend, terminate,
  create, execute agent, resume agent
  execution, resource management

(source 1)
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Agent Life Cycle
(source 1)
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• FIPA does not mandate a single form of agent
  mobility but supports a core set of actions that
  allow flexible and extensible forms of mobility
  protocols to be supported. Two example protocol
  abstractions

(source 1)

• Simple Mobility Protocol
• mobility supported by the AP
• simple agent development

• Full Mobility Protocol
• agent has enhanced control of the mobility
  operations
• more secure (?)

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Agent Support for Mobility (cont.)

• Agent profiles
• different agents have different
  demands/dependencies
• meta-information of an mobile agent (profile
  parameter)
• system
• Expresses requirements of the mobile agent
  system which the mobile agent uses (if any),
  such as Aglets, Mole, AgentTcl or Voyager
• language
• Expresses requirements of the language in which
  the mobile agent is written, such as Java source
  code, i386 native code or April byte-code
• os
• - requirements of the operating system for which
  the mobile agent was intended (if any), such as
  a Solaris SPARC box or a Linux i386 box
• Extra dependency information can be stated in
  the dependencies parameter of each profile
  description

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(source 1)

• FIPA Agent Message Transport specifications deal
  with the transport and representation of messages
  across different network transport protocols,
  including wireline and wireless environments
• Specifications
• Agent Message Transport Service
• Messaging Interoperability Service

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• FIPA ACL Message Representation specifications
  deal with different representation forms for ACL
  messages.
• Specifications ACL Message Representation in
• Bit-Efficient
• String
• XML

• FIPA Envelope Representation specifications deal
  with different representation forms for ACL
  message envelopes.
• Specifications Agent Message Transport
  Envelope Representation in
• Bit-Efficient
• XML

(source 1)

• FIPA Agent Message Transport Protocol (MTP)
  specifications deal with different network
  transport protocols for delivering ACL messages.
• Specifications Agent Message Transport
  Protocol for
• IIOP
• HTTP
• WAP

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(source 1)

• FIPA Application specifications are example
  application areas in which FIPA agents can be
  deployed. They represent ontology and service
  descriptions specifications for a particular
  domain.
• Specifications
• Nomadic Application Support
• Agent Software Integration
• Personal Travel Assistance
• Audio-Visual Entertainment and Broadcasting
• Network Management and Provisioning
• Message Buffering Service

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JADE

• A Java-based agent development framework
• A combination of two products
• A FIPA-Compliant Agent Platform
• A package to develop Java agents
• Includes the following agents
• AMS (Agent Management System)
• DF (Directory Facilitator)
• Sniffer
• RMA
• Includes features like
• library of FIPA interaction protocols
• automatic registration of agents with AMS
• FIPA-compliant naming service
• FIPA-compliant IIOP to connect to different AP-s
• GUI to manage several agents and AP-s

(FIPA-compliant AP)
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JADE Architecture

• Each agent lives inside a container
• A container
• is a JVM
• provides a complete runtime environment for
  agent execution
• allows several agents to run concurrently
• controls the life-cycle of agents (create,
  suspend, resume, kill)
• deals with communication (dispatches and routes
  messages)
• Light-weight container provided for agent
  execution within a web browser
• Special Container - the front-end (FE) container
• it runs the management agents
• it represents the whole platform to the outside
  world
• The GUI itself is implemented as an agent -
  Remote Management Agent (RMA)

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(source 2)
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Communication Subsystem

• The FE container includes an RMI registry used
  by other agent containers to join the AP
• The FE container maintains
• an Agent Container Table
• an Agent Global Descriptor Table (updated every
  time a container creates/destroys an agent)
• Each container maintains a cache of other
  containers object references
• references are added to cache as messages are
  sent
• Global Descriptor Table lookup for every message
  is avoided
• Agent containers transparently choose the most
  efficient available messaging mechanism,
  according to receiver agent location
• same container no remote invocations (clone()
  is called on ACL message object)
• same AP, different container, cache hit a
  single RMI call ACL message object is
  serialized/de-serialized by RMI runtime
• same AP, different container, cache miss two
  RMI calls 1. Update cache from Global Agent
  Descriptor Table 2. Send the message
• different AP (JADE) one IIOP call to remote AP
  plus the cost of one of the previous cases
• different AP (non-JADE) same as previous

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(source 2)
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Agent Execution Model

• Behavior - abstraction used to model the tasks
  that an agent is able to perform (for instance,
  multiple simultaneous conversations)
• Agents instantiate behaviors according to their
  needs and capabilities
• JADE uses the thread-per-agent concurrency model
  instead of a thread-per-behavior model in order
  to keep the number of threads small
• Agents extend from the base Agent class which
  implements a scheduler
• The scheduler carries out a round-robin
  non-preemptive policy among all behaviors
  available in the ready queue
• The execution of a Behaviour derived classes
  ends when the task itself relinquishes control
• Behaviors can be added/removed using Agents
  methods (addBehaviour(Behaviour),
  removeBehavior(Behavior))
• Developers can use existing behaviors provided
  by JADE or define their own classes, which need
  to extend Behavior and implement the abstract
  methods action() and done()

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(source 2)
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newer model (source 3)
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Problem Definition

• It implements a meeting scheduler agent that
  helps a user in scheduling meetings with other
  users.
• Contract-Net protocol is used to make a
  appointment.

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Contract-Net Protocol Support in JADE
Initiator createCfpContent
Responder handleCfpMessage
cfp
propose
refuse
Not-understood
Initiator handleProposeMessages handleOtherMessag
es
Responder handleAcceptProposalMessage handleReject
ProposalMessage
accept
reject
cancel
inform
failure
Initiator
Responder
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This Program

• It allows to try and check
• the registration of an agent with the default DF
  of the platform
• the registration of an agent with a remote DF
  belonging to another platform or, different from
  the default DF
• the search within the known DFs for a list of
  agents and their properties, in particular the
  list of MeetingScheduler agents and the name of
  the user that they represent
• the usage of the FipaContractNet protocol, both
  the initiator and responder role.

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JADE Demo
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• References
• FIPA Specifications - available at
  http//www.fipa.org/specifications
• The following documents are available at
  http//sharon.cselt.it/projects/jade/
• F.Bellllifemine at al., JADE - A FIPA-compliant
  agent framework in Proceedings of PAAM99, London,
  April 1999, pg.97-108
• Jade Programmer's Guide for JADE2.5, Feb.4th,
  2002
• Jade Administrator's Guide for JADE2.5, Jan.22nd,
  2002
• M.Laukkanen (Sonera Ltd.), Evaluation of JADE 1.2
• J. Ferber. Multi-agent Systems. An Introduction
  to Distributed Artificial Intelligence.
  Addison-Wesley, 1999.
• K. Carley, L. Gasser. Computational organization
  theories. In Multiagent Systems - A Modern
  Approach to Distributed Artficial Intelligence,
  G. Weiss (Ed.), The MIT Press, 2001, p.299-330.