Chapter 18 communication
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Chapter 18: Communication. Service-Oriented Computing: Semantics, Processes, Agents – Munindar P. Singh and Michael N. Huhns, Wiley, 2005. Highlights of this Chapter. Agent Communication Languages Communicative Act Theory Semantics Interaction Patterns Contract Net Protocol

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Chapter 18: Communication

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Chapter 18 communication

Chapter 18:Communication

Service-Oriented Computing: Semantics, Processes, Agents– Munindar P. Singh and Michael N. Huhns, Wiley, 2005


Highlights of this chapter

Highlights of this Chapter

  • Agent Communication Languages

    • Communicative Act Theory

    • Semantics

    • Interaction Patterns

  • Contract Net Protocol

  • Business Protocols

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Interaction and communication

Interaction and Communication

  • Interactions occur whenever agents share an environment

    • Resource contention, e.g., bumping into each other

  • Communications are interactions understood to preserve the participants’ autonomy

    • Realized by physical actions (e.g., shared memory or messaging middleware) that may not preserve autonomy

    • Meaning based on shared conventions

      • Offer loose coupling: essential for services

    • A message is a unit of communication

    • A protocol structures communications

      • What kind of structure is appropriate?

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Syntax semantics pragmatics

Syntax, Semantics, Pragmatics

  • Syntax: structure of a (communication) language

  • Semantics: meaning based solely on the terms used

    • Requires a structured vocabulary and a shared framework of knowledge, e.g., an ontology

  • Pragmatics: meaning based on the context (“here”)

    • Knowing whom to communicate with and how to find them

    • Knowing how to initiate and maintain an exchange

    • Knowing the effect of the communication on the recipient

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


A classification of message classifications

A Classification of Message Classifications

  • Structure-based (syntactic)

    • Distinguish messages based on grammatical forms in natural language

  • Meaning-based (semantic)

    • Distinguish messages based on a notion of intrinsic meaning

      • E.g., prohibitive is different from directive, despite syntactic similarity

  • Use-based (pragmatic)

    • Distinguish messages based on their functions in specific classes of protocols

      • E.g., assertion is different from acknowledgment

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Communicative act theory

Communicative Act Theory

Also called speech act theory (though not specific to speech)

  • Developed for human language

    • Views communication as action

    • Contrasts with traditional logic, which is about true or false assertions

  • Considers three aspects of a message:

    • Locution, or how it is phrased, e.g., “It is hot here” or “Turn on the air conditioner”: strings or XML documents

    • Illocution, or how it is meant by the sender or understood by the receiver, e.g., a request to turn on the air conditioner or an assertion about the temperature: message type plus proposition

    • Perlocution, or how it influences the recipient, e.g., turns on the air conditioner, opens the window, ignores the speaker

      Illocution is the core aspect

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Applying the theory

Applying the Theory

  • Classifications of illocutions motivate message types, but are typically designed for natural language

    • Rely on NL syntax, e.g., conflate directives and prohibitives

    • Address subtleties in natural language understanding: infer agents’ beliefs and intentions to determine which illocution

  • For networked services and multiagent systems, determining the

    • Message type is trivial, because it is explicitly encoded

    • Agents’ beliefs and intentions is impossible, because the internal details of the agents are not known

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Acl semantics

ACL Semantics

What does a inform, promise, request, query mean?

  • Mentalist: a state of solo or mutual beliefs or intentions (under assumption of sincerity)

    • Inform: speaker believes true

    • Promise: speaker intends to make true

    • Request: speaker intends listener to make true

    • Query: speaker intends listener to inform if true

  • Public: conventions based on laws and observations

    • Inform: speaker’s commitment to the veracity of

    • Promise: speaker’s commitment to bring about

      Evaluation: For open systems, public semantics is essential because it underlies compliance

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Chapter 18 communication

FIPA

FIPA is the Foundation for Intelligent Physical Agents

  • Incorporated as an IEEE standards body

  • Specifies standards for heterogeneous, interoperating agent-based systems

  • Concerned with agency as it relates to

    • Autonomous behavior

    • Communication with other agents

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Fipa standards support interoperability but at a low level

FIPA StandardsSupport interoperability, but at a low level

Ways of interpreting communications in a way that respects their intended meanings

  • Message types (called communicative acts): inform, request, …

  • Public ontologies

  • Transport and infrastructure

    • Superseded by Web services and messaging standards

  • Programming model and container

    • Compatible with containers in application servers

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Fipa standards provide

FIPA Standards Provide …

  • An architecture for interoperability

  • A few fixed primitives (message types)

    • Formal semantics based on mental notions

  • A few interaction protocols, but extensible

    • No formal semantics

    • Over-specified via low-level details

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Contract net protocol

Contract Net Protocol

An important generic protocol

  • Manager announces tasks via a (selective) multicast

  • Agents evaluate the announcement; some bid

  • Manager awards a contract to a bidder

  • Manager and contractor communicate privately as necessary

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Rfq task announcement

RFQ: Task Announcement

  • Eligibility specification: criteria that an agent must meet to be eligible to submit a bid

  • Task abstraction: a description of the task to be executed

  • Bid specification: a description of the expected format of the bid

  • Expiration time

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Bid and award messages

Bid and Award Messages

  • A bid specified the provider’s capabilities

  • An award consists of a task specification

    • A complete specification of the task

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Contract net evaluated

Contract Net Evaluated

  • Applies best when problem has a well-defined hierarchy of tasks

    • With coarse-grained decomposition

    • No interference with each other

    • Yields robustness: failure can be treated as a manifestation of autonomy

  • Lacks support for specifying service agreements and contracts

    • Purely operational

    • Hard-coded into the domain

    • Combines agent reasoning with interaction

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Commitment protocols

Commitment Protocols

  • Protocols expressed in terms of

    • Participants’ commitments

    • Actions for performing operations on commitments (to create and manipulate them)

    • Constraints on the above, e.g., captured in temporal logic

  • Examples: escrow, payment, RosettaNet (over 100 mostly request-response Partner Interface Processes or PIPs)

    • Traditionally, specified in operational terms

    • Can be expressed via commitments

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Netbill payment protocol

NetBill Payment Protocol

  • Checking compliance is easy but the representation is rigid

  • Some obvious variations are not allowed by the FSM:

    • The merchant may initiate the protocol by sending an offer

    • The customer may send an accept prior to offer

    • The merchant may send the goods prior to accept

    • How do we design a new FSM?

    • Verify it?

FSM Representation

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Netbill using commitments

NetBill using Commitments

Meanings:

1. true

2. request

3. offer

4. Cm,cgoods accept promiseReceipt

5. goods Cc,mpaypromiseReceipt

6. goods  pay Cm,creceipt

7. goods  pay  receipt

8. goods promiseReceipt

9. accept

Final states: all detached commitments are discharged

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Patterns for commitment operations

Patterns for Commitment Operations

  • Ensure that information about commitment operations flows to the right parties

    • To enable local decisions

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Complying with commitment protocols

Complying with Commitment Protocols

  • Compliance means commitments are discharged

    • Directly or indirectly after delegates and assigns

  • How can an agent check if others comply with specified protocols?

    • Agent x has grounds of complaint against agent y if and only if Cy,x(True, p), for some p

  • Commitment protocols are specified in terms of

    • Main roles and sphere of commitment

    • Roles essential for coordination

    • Domain-specific propositions and actions

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Verifying compliance

Verifying Compliance

  • Specification

    • Execution models based on potential causality

    • Commitments

  • Run-time verification (no access to implementations)

    • Respects heterogeneity

    • Local verification from observed messages: each party checks the others’ behavior

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Run time compliance checking

Run-Time Compliance Checking

  • An agent maintains

    • Pending commitments of which it is debtor or creditor

    • A local model: the messages sent or received

  • It uses this local model to verify that each commitment is discharged – or replaced by a commitment that is

  • Invariant: a creditor of a commitment can determine if it is violated – if the commitment doesn’t refer to a third party’s actions

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Fish market sample execution

Fish-Market Sample Execution

Based on a vector clock

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Fish market local observations

Fish-Market Local Observations

The discharge of a commitment must

be reachable from its create

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Fish market compliance

Fish-Market Compliance

  • Auctioneer can verify if the bidders comply

    • Sees each message as sender or receiver

  • An individual bidder cannot verify if the auctioneer complies

    • Doesn’t see each message

    • If bidders pool their observations, then they can verify if the auctioneer complies

  • Asymmetry indicates need for third party

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


Chapter 18 summary

Chapter 18 Summary

  • Communication enables loose coupling

  • Communications are actions – thus outside the purview of traditional logic

  • Protocols capture important patterns of communications

  • Business protocols can be understood using commitments

    • Model message meanings, not just syntax

    • Check compliance with respect to commitments

Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns


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