Agents Communication Languages (ACL)

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Agents Communication Languages (ACL)

• http//www.engr.uconn.edu/7Eibrahim/publications/
  acl.htm
• Dumitru Roman
• Digital Enterprise Research Institute
• dumitru.roman_at_deri.ie

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Outline

• Introduction
• Knowledge Query and Manipulation Language (KQML)
• Foundation for Intelligent Physical Agents (FIPA)
  ACL
• Comparing between KQML and FIPA
• Relevance to WSMO

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Introduction

• Motivation standard communication between
  heterogeneous agent communities.
• The origin of ACLs Knowledge Sharing Effort
  (KSE) - 1990
• software systems are virtual knowledge bases that
  exchange propositions using a language that
  expresses various complex attitudes -
  propositional attitudes - three part
  relationships between
• An agent,
• A content bearing proposition (for example, it is
  raining), and
• A finite set of propositional attitudes an agent
  might have with respect to the proposition (for
  example, believing, asserting, fearing,
  wondering, hoping, and so on).
• Example lta,fear,raining(t_now )gt

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Requirements of ACLs (1)

• Form an ACL should be
• Declarative, syntactically simple, and readable
  by people.
• Concise, easy to parse and to generate.
• Content
• A distinction should be made between the
  communication language, which expresses
  communicative acts, and the content language,
  which expresses facts about the domain.
• The language should commit to a well-defined set
  of communicative acts (primitives).
• Semantics - should be grounded in theory, and
  should be unambiguous.

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Requirements of ACLs (2)

• Implementation - should be efficient, both for
  speed, and for bandwidth utilization.
• Networking an ACL should fit well with modern
  networking technology.
• Environment an ACL must provide tools for
  coping with heterogeneity and dynamism and
  support interoperability with other languages and
  protocols.
• Reliability an ACL must support reliable and
  secure communication among agents.

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Requirements on agents to support ACL

• Agents should send not-understood (or error) if
  they receive a message that they do not recognize
  or they are unable to process the content of the
  message.
• An ACL compliant agent may choose to implement
  any subset of the pre-defined message types and
  protocols.
• An ACL compliant agent which uses the
  communicative acts whose names are defined in
  ACLs specification must implement them correctly
  with respect to their definition.
• Agents may use communicative acts with other
  names, and are responsible for ensuring that the
  receiving agent will understand the meaning of
  the act.
• An ACL compliant agent must be able to correctly
  generate a syntactically well-formed message in
  the transport form that corresponds to the
  message it wishes to send.
• In general, a content language must be able to
  express propositions, objects and actions.

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Basic concepts of ACL

• An ACL provides agents with a means of exchanging
  information and knowledge.
• The ACL itself defines the types of messages (and
  their meanings) that agents can exchange.
• Agents have conversationstask oriented, shared
  sequences of messages that they follow, such as a
  negotiation or an auction.
• The message types of ACLs - speech acts.

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Knowledge Query and Manipulation Language (KQML)

• A high-level, message-oriented communication
  language and protocol for information exchange
  independent of content syntax and applicable
  ontology.
• Three layers in a KQML message
• Content - bears the actual content of the message
  in the programs own representation language.
• Communication - encodes a set of features to the
  message that describe the lower-level
  communication parameters.
• Message - identify the network protocol with
  which to deliver the message and supply a speech
  act or perfomative that the sender attaches to
  the content.

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KQML Performatives

• A KQML message is called a performative.
• Parameters of a performative

sender - the actual sender of the performative. receiver - the actual receiver of the performative. from - the origin of the performative in content when forward is used. to - the final destination of the performative in content when forward is used. in-reply-to - the expected label in a response to a previous message (same as the value of the previous message). reply-with - the expected label in a response to the current message. language - the name of the representation language of the content. ontology - the name of the ontology (e.g., set of term definitions) assumed in the content parameter. content - the information about which the performative expresses an attitude.
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A KQML Message
A KQML Dialogue A to B (ask-if (gt (price bk1)
(price bk2))) B to A (reply true) B to A
(inform ( (price bk1) 25.50)) B to A (inform
( (price bk2) 19.99))
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KQML Performatives - Discourse performatives (1)

• ask-if - S wants to know if the content is in
  R's KB.
• ask-all - S wants all of R's instantiations of
  the content that are true of R.
• ask-one - S wants one of R's instantiations of
  the content that is true of R.
• stream-all - multiple-response version of
  ask-all.
• eos - the end-of-stream marker to a
  multiple-response (stream-all).
• tell - the sentence is in S's KB.
• untell - the sentence is not in S's KB.
• deny - the negation of the sentence is in S's KB.
• insert - S asks R to add the content to its KB

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KQML Performatives - Discourse performatives (2)

• uninsert - S wants R to reverse the act of a
  previous insert.
• delete-one - S wants R to remove one matching
  sentence from its KB.
• delete-all - S wants R to remove all matching
  sentences from its KB.
• undelete - S wants R to reverse the act of a
  previous delete.
• achieve - S wants R to do make something true of
  its physical environment.
• unachieve - S wants R to reverse the act of a
  previous achieve.
• advertise - S wants R to know that S can and will
  process a message like the one in content.
• unadvertise - S wants R to know that S cancels a
  previous advertise and will not process any more
  messages like the one in the content.

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KQML Performatives - Intervention and mechanics
of conversation performatives

• error - S considers R's earlier message to be
  mal-formed.
• sorry - S understands R's message but cannot
  provide a more informative response.
• standby - R will deliver its response to the S as
  soon as a response is generated.
• ready - S is ready to respond to a message
  previously received from R.
• next - S wants R's next response to a message
  previously sent by S.
• rest - S wants R's remaining responses to a
  message previously sent by S,
• discard - S does not want R's remaining responses
  to a previous (multi-response) message.

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KQML Performatives - Networking and Facilitation
performatives (1)

• register - S announces to R its presence and
  symbolic name.
• unregister - S wants R to reverse the act of a
  previous register.
• forward - S wants R to forward the message to the
  to agent (R might be that agent).
• broadcast - S wants R to send a message to all
  agents that R knows of.
• transport-address - S associates its symbolic
  name with a new transport address.

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KQML Performatives - Networking and Facilitation
performatives (2)

• broker-one - S wants R to find one response to
  the content (some agent other than R is going to
  provide that response).
• broker-all - S wants R to find all responses to
  the content (some agent other than R is going to
  provide that response).
• recommend-one - S wants to learn of an agent who
  may respond to the content.
• recommend-all - S wants to learn of all agents
  who may respond to the content.
• recruit-one - S wants R to get one suitable agent
  to respond to the content.
• recruit-all - S wants R to get all suitable
  agents to respond to the content.

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Semantics of KQML

• Semantics of each performative is defined in
  terms of
• preconditions - indicate the necessary states for
  an agent to send a performative and for the
  receiver to accept it and successfully process
  it.
• postconditions - describe the states of the
  sender after the successful utterance of a
  performative, and of the receiver after the
  receipt and processing of a message.
• completion conditions - indicate the final state,
  after a conversation has taken place and the
  intention associated with the performative that
  started the conversation has been fulfilled.

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Foundation for Intelligent Physical Agents (FIPA)
ACL

• Based on speech act theory messages are actions
  or communicative acts.
• Consists of a set of message types and the
  description of their pragmaticsthat is, the
  effects on the mental attitudes of the sender and
  receiver agents.
• Describes every communicative act with both a
  narrative form and a formal semantics based on
  modal logic.
• Separates the outer language (the intended
  meaning of the message) from the inner language
  (content language).
• The communication primitives are called
  communicative acts.

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ACL Message
Note FIPA uses a different content language
from KQML called SL, which is based on modal
logic.
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FIPA - Communicative Acts (1)

• accept-proposal - The action of accepting a
  previously submitted proposal to perform an
  action.
• agree - The action of agreeing to perform some
  action, possibly in the future.
• cancel - The action of cancelling some previously
  request'ed action which has temporal extent (i.e.
  is not instantaneous).
• cfp - The action of calling for proposals to
  perform a given action.
• confirm - The sender informs the receiver that a
  given proposition is true, where the receiver is
  known to be uncertain about the proposition.
• disconfirm - The sender informs the receiver that
  a given proposition is false, where the receiver
  is known to believe, or believe it likely that,
  the proposition is true.
• failure - The action of telling another agent
  that an action was attempted but the attempt
  failed.
• inform - The sender informs the receiver that a
  given proposition is true.

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FIPA - Communicative Acts (2)

• inform-if - A macro action for the agent of the
  action to inform the recipient whether or not a
  proposition is true.
• inform-ref - A macro action for sender to inform
  the receiver that an object corresponds to a
  definite descriptor (e.g. a name).
• not-understood - The sender of the act (e.g. i)
  informs the receiver (e.g. j) that it perceived
  that j performed some action, but that i did not
  understand what j just did.
• propose - The action of submitting a proposal to
  perform a certain action, given certain
  preconditions.
• query-if - The action of asking another agent
  whether or not a given proposition is true.
• query-ref - The action of asking another agent
  for the object referred to by an expression.
• refuse - The action of refusing to perform a
  given action, and explaining the reason for the
  refusal.

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FIPA - Communicative Acts (3)

• reject-proposal - The action of rejecting a
  proposal to perform some action during a
  negotiation.
• request - The sender requests the receiver to
  perform some action. One important class of uses
  of the request act is to request the receiver to
  perform another communicative act.
• request-when - The sender wants the receiver to
  perform some action when some given proposition
  becomes true.
• request-whenever - The sender wants the receiver
  to perform some action as soon as some
  proposition becomes true and thereafter each time
  the proposition becomes true again.
• request-whomever - The sender wants an action
  performed by some agent other than itself. The
  receiving agent should either perform the action
  or pass it on to some other agent.
• subscribe - The act of requesting a persistent
  intention to notify the sender of the value of a
  reference, and to notify again whenever the
  object identified by the reference changes.

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Semantics of FIPA ACL

• SL (Semantic Language) it can represent
  propositions, objects, and actions.
• Semantics of each communicative act is specified
  as sets of SL formulae that describe the acts
• feasibility pre-conditions - describe the
  necessary conditions for the sender of the CA.
• rational effect - represents the effect that an
  agent can expect to occur as a result of
  performing the action it also typically
  specifies conditions that should hold true of the
  recipient.

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Comparing KQML and FIPA ACL (1)

• Almost identical with respect to their basic
  concepts and the principles they observe.
• Differ primarily in the details of their semantic
  frameworks.
• KQML and FIPA ACL messages look syntactically
  identical.
• Difference in their treatment of the registration
  and facilitation primitives.

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Comparing KQML and FIPA ACL (2)

• agent management
• KQML register, unregister, recommend, broker,
  recruit, advertise.
• FIPA considers these to be services offered by
  the basic agents in a system, rather than message
  types.
• communications management
• KQML broadcast, transport-address, forward.
• FIPA considers these to be services offered by
  the basic agents in a system, rather than message
  types.
• multiple solutions
• KQML ask-one, ask-all, stream-all, eos, standby,
  ready, next, rest, discard.
• FIPA does not express these concepts in the ACL,
  but in the content of the ACL messages.
• direct belief manipulation
• KQML insert, uninsert, delete-one, delete-all.
• FIPA has no equivalent of these, since agents are
  not given the power to directly manipulate the
  beliefs of other agents.
• goal definition
• KQML acheive, unacheive.
• FIPA does not express these concepts in the ACL,
  but in the context of the ACL messages.

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Relevance to WSMO

• Consider the idea of speech acts for simple MEP
  in WSMO
• FIPA ACL request
• FIPA ACL inform
• FIPA ACL failure
• Consider WSML as the content language