chapter 18 communication
Download
Skip this Video
Download Presentation
Chapter 18: Communication

Loading in 2 Seconds...

play fullscreen
1 / 26

Chapter 18: Communication - PowerPoint PPT Presentation


  • 115 Views
  • Uploaded on

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

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Chapter 18: Communication' - felix


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
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

slide9
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

ad