Multiagent Systems Service-Oriented Computing: Semantics, Processes, Agents – Munindar P. Singh...

Multiagent Systems

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

Chapter 16 2Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns

Highlights of this Section

Applicability in Service-Based Systems

Multiagent Architecture Agent Types Lifecycle Management Consistency Maintenance Modeling Other Agents Cognitive Concepts


Michael Huhns

Attributes of Multiagent Systems

Decentralization: agents are autonomous

Complex constituents (business partners modeled as agents), often best described at the knowledge level

Adaptive behavior Complex interactions Coordination Emergent, aggregate behaviors


Michael Huhns

Dimensions of MAS: AgentAdaptivity (the ability of an agent to learn):

Autonomy:

Interactions:

Sociability (awareness):

Fixed Teachable Autodidactic

Controlled Independent

Simple Complex

Interdependent

Autistic CollaborativeCommitting


Michael Huhns

Dimensions of MAS: System

Scale (the number of agents):

Interactions:

Coordination (self interest):

Agent Heterogeneity:

Communication Paradigm:

Individual Committee Society

Reactive Planned

Antagonistic AltruisticCollaborative

Competitive Cooperative Benevolent

Identical Unique

Point-to-Point Multi-by-name/role Broadcast


Michael Huhns

Basic Problems of MAS

Distribution of control among agents Description, decomposition, and

distribution of tasks among agents Interaction and communication

among agents Representation of goals, problem-

solving states, and other agents Rationality, consistency

maintenance, and reconciliation of conflicts among agents


Michael Huhns

Principles of Multiagent Systems System architecture Low-level interoperation Information systems

Description: ontologies Engagement: transactions

Protocols and compliance Frameworks that support the

necessary abstractions


Michael Huhns

(de facto) Standard Agent Types

User AgentsApplication Programs

Directory and BrokerAgents

Execution or DataManager Agents

Ontology Agents

Database ResourceAgents

Internet Data Agents

Structured DataUnstructured Data


Michael Huhns

Name Service

A multiagent architecture requires scalable, symbolic name resolution

Alternative naming approaches FIPA LDAP Jini CORBA Naming Service JNDI


Michael Huhns

Directory Service Simple yellow-page service Registered agents advertise their services by

providing their name, address, and service description

Agents request recommendations for available services (provided by other registered agents or services)

A simple database-like mechanism that allows agents to

Insert descriptions of the services they offer Query for services offered by other agents.

1..n Directory Service Agents on a LAN Brokerage, recruitment and mediation services

are not provided by Directory Service


Michael Huhns

Agent Framework Services (CoABS)

Agent Ausing KQML

or ICL

Agent Busing FIPA

ACL

Agent Cusing KQML

or ICL

GridAdapter Library

Translation

MessageHandling

GridProxy

Translation

MessageHandling

InterprocessCommunication




FIPA Agent Managementand ACL Specifications

Other CoABS ComponentsRETSINA

MatchMaker

Naming Directory Logging

Translating Brokering Visualizing


Michael Huhns

Brokerage Service Beyond UDDI

Cooperates with a Directory Service An agent requests the Brokerage Service to

recruit one or more agents who can provide a service

Brokerage Service uses knowledge about the requirements and capabilities of registered agents to

Determine the appropriate agents to which to forward a request for a service

Negotiates with the agents to determine a suitable set of service providers

Potentially learn about the properties of the responses

example: Brokerage agent determines that advertised results from agent X are incomplete and seeks a substitute for X


Michael Huhns

FIPA Agent Management System

Software

AgentAgent

ManagementSystem

DirectoryFacilitator

Message Transport System

Message Transport System

Agent Platform

Agent Platform

Platform Services


Michael Huhns


Michael Huhns

Agent Management System: 2

Handles the creation, registration, location, communication, migration and retirement of agents. Provides the following services:

White pages, such as agent location, naming and control access services, which are provided by the Agent Management System (AMS). Agent names are represented by a flexible and extensible structure called an agent identifier, which can support social names, transport addresses, name resolution services, amongst other things

Yellow pages, such as service location and registration services, which are provided by the Directory Facilitator (DF)

Agent message transport services

Standard Components of the FIPA Communication Model


Michael Huhns


Michael Huhns

Java Agent Development Framework

JADE, the most popular, FIPA-compliant agent framework for multiagent systems: http://jade.tilab.com/ The most established of the publicly

available agent frameworks FIPA-OS and Zeus having died


Michael Huhns

Consistency Maintenance across Services

A truth maintenance system (TMS) supports maintaining consistency

performs a form of propositional deduction maintains justifications and explains the

results of its deductions updates beliefs incrementally when data are

added or removed uses its justifications to perform dependency-

directed backtrackingTMSs are important because they deal with atomicity deal with the frame problem lead to efficient search


Michael Huhns

Architecture of TMS-Based Agent

The problem solver represents domain knowledge in the form of rules, procedures, etc. and chooses what to focus on next

The TMS keeps track of the current state of the search for a solution. It uses constraint satisfaction to maintain consistency in the inferences made by the problem solver

ProblemSolver

TMS

justifications

beliefs


Michael Huhns

Knowledge Base Integrity

Stability: believe everything justified validly; disbelieve everything justified invalidly

Well-Foundedness: beliefs are not circular

Logical consistency: logical contradictions do not exist

Completeness: a system will find a consistent state if it exists, or report failure

Problems arise when knowledge is distributed


Michael Huhns

Degrees of Logical Consistency Inconsistency: an agent is individually

inconsistent Local Consistency: all agents are

individually consistent Local-and-Shared Consistency: agents

are locally consistent and agree about any data they might share

Global Consistency: agents are globally consistent (union of KBs is consistent)

The DTMS maintains local-and-shared consistency and well foundedness


Michael Huhns

Distributed TMS Each agent has a justification-based TMS Each datum can have status OUT, IN (valid

local justification), or EXTERNAL. A shared datum must be IN to one of the agents that shares it

When a problem solver adds or removes a justification, the DTMS

Unlabels data based on the changed justification

Labels all unlabeled shared data Chooses labels for remaining unlabeled data; if

this fails, it backtracks by unlabeling additional data and iterating


Michael Huhns

Cooperative Service: 1

Clientf3: afford(xcorp) INr3: buy(X) :- query(Broker recommend(X)),

afford(X) IN

Brokerf1: afford(xcorp) OUTf2: cash-rich(xcorp) INr2: recommend(X) :- takeover-bid(X) INr1: takeover-bid(X) :- cash-rich(X) IN

? recommend(?X)


Michael Huhns



afford(X) IN

Brokerf1: afford(xcorp) OUTf2: cash-rich(xcorp) INr1: recommend(X) :- takeover-bid(X) INr2: takeover-bid(X) :- cash-rich(X) INf3: recommend(xcorp) IN

Shared with: Client; Justification: (f2 r1 r2)

recommend(XCorp)


Michael Huhns



afford(X) INf4: recommend(xcorp) EXTERNAL

Shared with: Broker; Justification: ( )f5: buy(xcorp) IN

Justification: (f3 f4 r3)

Brokerf1: afford(xcorp) OUTf2: cash-rich(xcorp) INr1: recommend(X) :- takeover-bid(X) INr2: takeover-bid(X) :- cash-rich(X) INf3: recommend(xcorp) IN



Michael Huhns



afford(X) INf4: recommend(xcorp) EXTERNAL

Shared with: Broker; Justification: ( )f5: buy(xcorp) IN


Brokerf1: afford(xcorp) OUTf2: cash-rich(xcorp) IN --> OUTr1: recommend(X) :- takeover-bid(X) INr2: takeover-bid(X) :- cash-rich(X) INf3: recommend(xcorp) IN --> OUT


relabel recommend(XCorp)


Michael Huhns



afford(X) INf4: recommend(xcorp) OUT

Shared with: Broker; Justification: ( )f5: buy(xcorp) OUT


Brokerf1: afford(xcorp) OUTf2: cash-rich(xcorp) OUTr1: recommend(X) :- takeover-bid(X) INr2: takeover-bid(X) :- cash-rich(X) INf3: recommend(xcorp) OUT



Michael Huhns

Cognitive Economy Prefer the simpler (more economical) explanation ("but

not too simple" - Einstein)

Essential because agents have limited reasoning capacities

Agents must finitely represent their environment themselves and others themselves and others representing them and others, ad

infinitum Zero-order model: others are similar to oneself


Michael Huhns

“Practical” Economy

In simple terms, cognitive economy has two consequences on how agents act Agents should act predictably Agents should act the way they want

others to act These are examples of

universalizable principles as advocated by Kant, and provide a rational basis for ethical and social behavior


Michael Huhns

Challenges

Doing the "right" thing Autonomy Conventions: emergence and

maintenance Coordination Collaboration Communication: semantics and

pragmatics Interaction-oriented programming


Michael Huhns

Section Summary

Study multiagent systems because interactions among agents make them interesting

Communication among agents is key, although markets (later chapter) only support implicit communication through prices

Programming environments support agent interactions

Consistency maintenance is a major challenge

Agents must model agents; simple techniques are often adequate; more subtle techniques can require extensive reasoning power

Organizations


33Chapter 17Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns


Contracts Spheres of Commitment Achieving Collaboration via

Conventions Policies Negotiation


Michael Huhns

Why Organizations?

Serious applications of services require interactions structured in subtle ways

Organizations consist of agents (business partners) providing or using services

Organizations Relate well to human organizations Promote coherence in service interactions Offer a conceptually natural, high-level

basis for understanding and designing service interactions


Michael Huhns

Organizations

Organizations are naturally nested (not necessarily as trees) All organizations are

agents Some agents are

organizations Organizations help

overcome the limitations of individuals in Reasoning Capabilities Perception Lifetime and persistence


Michael Huhns

Three Kinds of Organizations

Concrete: organizations consist of agents playing roles Configured, run-time concept

Abstract (templates): organizations consist of roles and relationships among roles Design-time concept

Institutions: part abstract and part concrete Run-time concept, but the membership can

change Example: eBay, where buyers and sellers can

change but eBay itself is a fixed participant


Michael Huhns

Legal Abstractions

Contracts Directed obligations Hohfeldian concepts Compliance


Michael Huhns

Contracts

Much of the law is about the creation and manipulation of contracts among legal entities People Corporations Governmental agencies

Key questions: how to create, modify, perform, or monitor contracts


Michael Huhns

Motivation for Contracts

Provide a basis for service agreements

Crucial in open environments Constrain behavior: limit autonomy to

some extent Emphasize behavior: observable by

others Mostly disregard internal

implementations, thus facilitating heterogeneity


Michael Huhns

Legal Concepts

Rich in multiagent concepts Inherently about interactions

among autonomous parties Directed obligations

One party being obliged to another party

Multiagent flavor Contrast with traditional deontic

logic Zero-agent: it is obliged that … One-agent: you are obliged to do …


Michael Huhns

Rights

The rights or claims a party has on another party Not the right (ethical) thing to do

The claims of one party are the duties of another: claim is a correlate of duty


Michael Huhns

Hohfeldian Concepts: 1

The term “right” is used ambiguously

Sixteen concepts distinguish the main situations: Four main concepts Their correlates Their negations Their negations’ correlates


Michael Huhns

Hohfeldian Concepts: 2

Claim-duty: as above Privilege-exposure: freedom from

the claims of another agent Power-liability: when an agent can

change the claim-duty relationship of another agent

Immunity-disability: freedom from the power of another agent


Michael Huhns

Commitments

Commitments are a three-party concept An agent’s commitment to another agent

occurs within a context (usually organizational) Is unidirectional Arises within a well-defined scope or context May be manipulated Enables coordination through the ordering

and occurrence of actions by the agents Commitments are public (unlike beliefs) Commitments provide a basis for

compliance


Michael Huhns

Manipulating Commitments

Operations on commitments: Create Discharge (satisfy) Cancel Release (eliminate) Delegate (change debtor) Assign (change creditor)

Metacommitments constrain the manipulation of commitments


Michael Huhns

Commitments for Contracts

A contract is a set of related commitments Provides context to the commitments Applies between specified parties, in a

context (e.g., UCC, real-estate, Internet commerce)

In contrast to commitments, other approaches: Single-agent focused, e.g., deontic logic Don’t handle organizational aspects of

contracts Don’t accommodate manipulation of

contracts


Michael Huhns

SoCom: Sphere of Commitment

A computational abstraction based on organizations

An organization that provides the context or scope of commitments Involves roles (abstract) or agents

(concrete) Serves as a witness for the commitment,

i.e., knows that the commitment exists Serves as a place to test for compliance Serves as a locus for policies on

enforcement and compensation

- Munindar Singh and Michael Huhns

SoComs and Structure

SoCom inherit policies from surrounding (contextual) SoCom UCC applies to commercial

interactions Inherited policies can conflict because

of Nonunique nesting When agents play multiple roles


Michael Huhns

Virtual Enterprises (VE)

A VE offers additional commitments beyond what its members individually offer

Sellers come together with a new proxy agent called VE

Example of VE agent commitments: Notify on change Update orders Guarantee the price Guarantee delivery

date


Michael Huhns

A Selling VE (Composition Example)Customer Virtual Enterprise Hose Seller Valve Seller

I would like to buy a valve with inputdia of 43, two matching hoses, andof price up to $50.00

Order placed; 1 valve idia = 43Odia = 43. 2 hoses dia = 43Charge = $14.83 Sell two 43 dia hoses

Order is ready

Order revised; 1 valve idia = 43odia = 21, hose dia = 43, andhose dia = 21. Charge = $14.83

Order processed

valve input dia = 43, output dia 43 discontinuedvalve input dia = 43, output dia 21 recommended

Cancel previous order

Sell one valve with input dia 43, output dia 21

Order is ready

Yes

Two 43 dia hoses in stock?

One valve with input dia 43, output dia 43 in stock?

Yes

One 43 dia & one 21dia hose in stock?

Yes

Sell one 43 dia & one 21dia hose

Order is ready


Michael Huhns

Teams

Tightly knit organizations Shared goals, i.e., goals that all

team members have Commitments to help team-

members Commitments to adopt additional

roles and offer capabilities on behalf of a disabled member


Michael Huhns

Teamwork

When a team carries out some complex activity Negotiating what to do Monitoring actions jointly Supporting each other Repairing plans


Michael Huhns

Negotiation

Negotiation is central to adaptive, cooperative behavior

Negotiation involves a small set of agents

Actions are propose, counterpropose, support, accept, reject, dismiss, retract

Negotiation requires a common language and common framework (an abstraction of the problem and its solution)


Michael Huhns

Negotiation Mechanism Attributes

Efficiency Stability Simplicity Distribution SymmetryE.g., sharing book purchases, with

cost decided by coin flip


Michael Huhns

Negotiation among Utility-Based Agents

Problem: How to design the rules of an environment so that agents interact productively and fairly, e.g.,

Vickrey’s Mechanism: lowest bidder wins, but gets paid second lowest bid (this motivates telling the truth?? and is best for the consumer??)


Michael Huhns

Negotiation

A deal is a joint plan between two agents that would satisfy their goals

The utility of a deal for an agent is the amount he is willing to pay minus the cost to him of the deal

The negotiation set is the set of all deals that have a positive utility for every agent. The possible situations for interaction are

Conflict: the negotiation set is empty Compromise: agents prefer to be alone, but will

agree to a negotiated deal Cooperative: all deals in the negotiation set are

preferred by both agents over achieving their goals alone


Michael Huhns

Negotiation Mechanism

The agents follow a Unified Negotiation Protocol, which applies to any situation. In this protocol,

The agents negotiate on mixed-joint plans, i.e., plans that bring the world to a new state that is better for both agents

If there is a conflict, they “flip a coin” to decide which agent gets to satisfy his goal


Michael Huhns

Problem Domain Hierarchy

Worth-Oriented Domains

State-Oriented Domains

Task-Oriented Domains


Michael Huhns

Task-Oriented Domains: 1

A TOD is a tuple <T, A, c>, where T is the set of tasks, A is the set of agents, and c(X) is a monotonic function for the cost of executing the set of tasks X

Examples Deliveries: c(X) = length of minimal path that

visits X

Postmen: c(X) = length of minimal path plus return

Databases: c(X) = minimal number of needed DB ops


Michael Huhns

Task-Oriented Domains: 2

A deal is a redistribution of tasks Utility of deal d for agent k is

Uk (d) = c(Tk) - c(dk) The conflict deal, D, is no deal A deal d is individual rational if d>D Deal d dominates d’ if d is better for at least

one agent and not worse for the rest Deal d is Pareto optimal if there is no d’>d The set of all deals that are individual rational

and Pareto optimal is the negotiation set, NS


Michael Huhns

Monotonic Concession Protocol Each agent proposes a deal If one agent matches or exceeds what

the other demands, the negotiation ends

Else, the agents propose the same or more (concede)

If no agent concedes, the negotiation ends with the conflict dealThis protocol is simple, symmetric, distributed, and guaranteed to end in a finite number of steps in any TOD. What strategy should an agent adopt?


Michael Huhns

Zeuthen Strategy

Offer deal that is best among all deals in NS Calculate risks of self and opponent

R1=(utility A1 loses by accepting A2’s offer) (utility A1 loses by causing a conflict)

If risk is smaller than opponent, offer minimal sufficient concession (a sufficient concession makes opponent’s risk less than yours); else offer original deal

If both use this strategy, they will agree on deal that maximizes the product of their utilities (Pareto optimal)

The strategy is not stable (when both should concede on last step, but it’s sufficient for only one to concede, then one can benefit by dropping strategy)


Michael Huhns

Deception-Free Protocols

Zeuthen strategy requires full knowledge of

Tasks Protocol Strategies Commitments

Hidden tasks Phantom tasks Decoy tasks

P.O. A1 (hidden)

A1 A2


Michael Huhns

Section Summary

Organizations are a natural metaphor for understanding and designing systems of services

Organizations provide a basis for Legal and contractual concepts such

as commitments Teamwork Understanding and formalizing

negotiation

Communication



Michael Huhns


Agent Communication Languages Speech Act Theory Semantics Interaction Patterns

Combining ACLs with Web Services Contract Net Protocol Business Protocols


Michael Huhns

Interaction and Communication

Interactions occur whenever agents share an environment

Resource contention, e.g., bumping into each other Communications are interactions understood

so as to preserve autonomy of all participants A way to achieve loose coupling: essential for

services Meaning captured through shared conventions

Communications are realized through physical actions that may not preserve autonomy

Through shared memory or messaging middleware, but we use the term message for a unit of communication


Michael Huhns

Syntax, Semantics, Pragmatics

Syntax: a common language to represent information and queries, or languages that are intertranslatable

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


Michael Huhns

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


Michael Huhns

Speech Act TheoryCommunicative act theory (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


Michael Huhns

Speech Act Theory Applied

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

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

In natural language understanding: determining the how locutions map to illocutions (inferring agents’ beliefs and intentions)

For services and agents, 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


Michael Huhns

ACL Semantics

What is the semantics of queries, requests, promises?

Mentalist: meaning based on participants’ knowledge bases

An agent promises something if it intended to make that promise

Usually accompanied by assumption of sincerity Public: semantics depends on laws, protocols,

and observable behavior An agent promises something if it says so in the

appropriate circumstances

Evaluation: For open systems, public semantics is more appropriate, because being able to determine compliance is essential


Michael Huhns

FIPA

FIPA is the Foundation for Intelligent Physical Agents, with website at www.fipa.org

Moved into IEEE Specifies standards for heterogeneous,

interoperating agent-based systems Concerned with agency as it relates to

Autonomous behavior Communication with other agents


Michael Huhns

FIPA Standards

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

Communicative acts Public ontologies Transport and infrastructure

Superseded by Web services and messaging standards

Programming model and container Compatible with containers in application servers

Compared to existing approaches XML Schema standardizes grammar, not

meaning OWL standardizes ontology description, not

communication


Michael Huhns

Low-Level Patterns

Requester

Requester

Requester

Provider

Provider

Provider

Synchronous: a blocking query waits for an expected reply

Provider maintains state; replies sent individually when requested

Asynchronous: a nonblocking subscribe; replies sent as available

Query

Reply

Next

Handle

Query

Reply

Next

Reply

Subscribe

Reply

Reply

Reply


Michael Huhns

Combining Agents with Traditional Web Services

WebService Agent

Gateway

Web ServiceClient

SOAPRequest

SOAPResponse

Agent

ACLRequest

ACLInform

ACL is the FIPA ACL standard


Michael Huhns

Contract Net Protocol: 1

An important generic protocol

Manager announces tasks via a (possibly selective) multicast

Agents evaluate the announcement; some submit bids

Manager awards a contract to the most appropriate bidder

Manager and contractor communicate privately as necessary


Michael Huhns

Contract Net: 2

The Contract Net Applies best when problem has a

well-defined hierarchy of tasks With coarse-grained decomposition No interference among each other

Lacks support for specifying service agreements and contracts

Yields robustness: failure can be treated as autonomy


Michael Huhns

RFQ: Task Announcement

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

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

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

Expiration time: a statement of the time interval during which the task announcement is valid


Michael Huhns

Bid and Award Messages

A bid specified the provider’s capabilities

An award consists of a task specification A complete specification of the task


Michael Huhns

Commitment Protocols

Protocols enable open systems to be constructed

Interaction 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 (107 mostly request-response Partner Interface Processes or PIPs)


Michael Huhns

NetBill Payment Protocol Checking compliance is

easy but the representation is rigid

Some obvious variations are not allowed by the FSM:

The merchant may start the protocol by sending a quote

The customer may send an accept prior to offer

The merchant may send the goods prior to accept

FSM Representation

C: rfq

M: offer

C: accept

C: pay

M: receipt

M: goods


Michael Huhns

NetBill Enhanced by CMs

Meanings:

1. true

2. request

3. offer

4. Cmgoods accept promiseReceipt

5. goods Ccpay promiseReceipt

6. goods pay Cmreceipt

7. goods pay receipt

8. goods promiseReceipt

9. accept

Final state: No open commitments remain

C: rfq

M: offer

C: accept

C: pay

M: receipt

M: goods

M: offer

M: goods

C: pay

C: accept

M: g

oods


Michael Huhns

Message Patterns for Commitment Operations

Ensure that information about commitment operations flows to the right parties, to enable local decisions

x y z

create(x,c)

delegate(x,z,c)

delegate(x,z,c)

discharge(x,c)

x y z

create(x,c)

assign(x,y,z)

discharge(x,c)

assign(x,y,z)


Michael Huhns

Complying with Commitment Protocols

Compliance means commitments are taken care of (discharged directly or indirectly)

How can an application check if the agents comply with specified protocols?

Commitment protocols are specified in terms of

Main roles and sphere of commitment Roles essential for coordination Domain-specific propositions and

actions


Michael Huhns

Verifying Compliance

Specification Models based on potential causality Commitments based on branching-

time TL Run-time Verification

Respects design autonomy Uses TL model-checking Local verification based on observed

messages: each party checks if the others are behaving appropriately


Michael Huhns

Run-Time Compliance Checking

An agent can keep track of Its pending commitments Commitments made by others that are not

satisfied It uses this local model to see if a

commitment has been violated All commitments must eventually be

discharged or replaced by commitments that are …

An agent who benefits from a commitment can always determine if it was violated


Michael Huhns

Fish-Market Sample Execution

Auctioneer A Bidder B1

m1 “50”: [1,0,0]

m3 “No”: [1,2,0]

m5 “40”: [5,2,2]

m8 “No”: [6,2,4]

Bidder B2

m2 “50”: [2,0,0]

[0,0,0] [0,0,0] [0,0,0]

[2,0,1]

[4,2,2]

[3,2,0]

[5,3,2]

m6 “40”: [6,2,2] [6,2,3]

m7 “Yes”: [5,4,2][7,4,2]

fishmoney

[1,1,0]

[8,4,4]

m4 “No”: [2,0,2]

Based on a vector clock


Michael Huhns

Fish-Market Local Observations

Auctioneer A

[1,0,0]

[2,0,0]

[3,2,0]

[4,2,2]

start

s(m1)

s(m2)

s(m4)

r(m3)

r(m4)

[2,0,2]

[5,2,2]

[6,2,2]

[7,4,2]

end

s(m5)

s(m6)

r(m7)

Bidder B1

start

s(m1)

[1,0,0]

r(m1)

s(m3)

r(m5)

s(m7)

end

[1,1,0]

[1,2,0]

[5,2,2]

[5,3,2]

[5,4,2]

s(m5)

The discharge of a commitment mustbe reachable from its create


Michael Huhns

Fish-Market Compliance

Auctioneer can verify if the bidders comply

An individual bidder cannot verify if the auctioneer complies

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

Asymmetry indicates need for third party


Michael Huhns

Section Summary Communication is a key form of

interaction Communications are actions – thus

outside the purview of traditional logic Protocols capture important patterns of

communications Business protocols can be understood

using commitments Modeling captures their meaningful content,

not just message tokens Commitments provide a basis for checking

compliance

Multiagent Systems Service-Oriented Computing: Semantics, Processes, Agents – Munindar P. Singh...

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