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Chapter 17:Organizations

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

Chapter 17 2Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and

Michael Huhns

Highlights of this Chapter Contracts Spheres of Commitment Policies Negotiation


Michael Huhns

Why Organizations? 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 nest, though

usually not as trees All organizations are

agents Some agents are

organizations Organizations help overcome

limitations of individuals in Reasoning Capabilities Perception Lifetime, persistence


Michael Huhns

Three Kinds of Organizations

Concrete: agents playing roles Configured, run-time concept

Abstract (templates): 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 as Service Agreements Contracts structure interactions

(i.e., service engagements) among autonomous parties People and corporations Governmental agencies

Compare with contracts in programming Each needs a computational

representationKey questions: how to create,

modify, perform, or monitor contracts


Michael Huhns

Motivation for Contracts Provide a basis for service

agreements Crucial in open environments Emphasize public behavior:

observable by others Constrain behavior: limit autonomy Mostly disregard internal

implementations, thus supporting heterogeneity

May expose some implementation


Michael Huhns

Legal Concepts Inherently multiagent: 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 obligatory 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 A commitment

Involves three parties: a debtor commits to a creditor within an organizational context

Is scoped by its (organizational) context May be manipulated, subject to additional

commitments Is public (unlike beliefs)

Commitments provide Flexible interactions, thus promoting

coherence A basis for judging 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 a notional 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 institution with additional features Involves roles (abstract) or agents

(concrete) A witness for the commitment

Trusted party to decide satisfaction or violation

A locus for testing compliance and enforcing corrections (e.g., compensation)

- Munindar Singh and Michael Huhns

SoComs and Structure A SoCom inherits policies from

surrounding (contextual) SoCom E.g., 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 commitments

beyond those of its members to support business atomicity

Sellers come together with a new proxy agent called VE

Example of VE agent commitments: Entertain order updates Notify on change of

order Price guarantee Delivery date

guarantee


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 Goals shared by all team members 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 each bidder to bid its

true valuation


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 StrategyOffer 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

Chapter 17 Summary Organizations are a natural

metaphor for understanding and designing systems of services

Organizations provide a basis for realizing coherent interactions Legal and contractual concepts such

as commitments Teamwork Understanding and formalizing

negotiation

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