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Multi-Agent Systems

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Title: Multi-Agent Systems


1
Multi-Agent Systems
  • University Politehnica of BucarestSpring
    2010http//turing.cs.pub.ro/mas_10curs.cs.pub.r
    o

2
JADE - A FIPA-Compliant Java Agent Development
Framework
3
Outline
  • FIPA Specifications
  • The JADE Platform
  • Jade In Action - Demo

4
  • 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)
5
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)
6
(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

7
(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)
8
Interaction Protocols(2/3)
(source 1)
9
Interaction Protocols(3/3)
(source 1)
(source 1)
10
(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

Andrei Dancus
11
(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

12
  • 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
13
(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

14
  • 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

Agent Management
(source 1)
15
Agent Life Cycle
(source 1)
16
  • 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 (?)

17
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

18
(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

19
  • 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

20
(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

21
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)
22
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)

23
(source 2)
24
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 containercreates/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

25
(source 2)
26
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()

27
(source 2)
28
newer model (source 3)
29
JADE Demo
30
References
1 FIPA Specifications - available at
http//www.fipa.org/specifications all documents
below are available at http//sharon.cselt.it/proj
ects/jade/ 2 F.Bellllifemine at al., JADE - A
FIPA-compliant agent framework in Proceedings of
PAAM99, London, April 1999, pg.97-108 3 Jade
Programmer's Guide for JADE2.5, Feb.4th, 2002 4
Jade Administrator's Guide for JADE2.5, Jan.22nd,
2002 5 M.Laukkanen (Sonera Ltd.), Evaluation of
JADE 1.2
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