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

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Presentation on theme: "Multiagent Systems Service-Oriented Computing: Semantics, Processes, Agents – Munindar P. Singh and Michael N. Huhns, Wiley, 2005."— Presentation transcript:

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

2 Chapter 162Service-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

3 Chapter 163Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

4 Chapter 164Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Dimensions of MAS: Agent Adaptivity (the ability of an agent to learn): Autonomy: Interactions: Sociability (awareness): FixedTeachableAutodidactic ControlledIndependent SimpleComplex Interdependent AutisticCollaborativeCommitting

5 Chapter 165Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Dimensions of MAS: System Scale (the number of agents): Interactions: Coordination (self interest): Agent Heterogeneity: Communication Paradigm: IndividualCommitteeSociety ReactivePlanned AntagonisticAltruisticCollaborative CompetitiveCooperativeBenevolent IdenticalUnique Point-to-PointMulti-by-name/roleBroadcast

6 Chapter 166Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

7 Chapter 167Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

8 Chapter 168Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns (de facto) Standard Agent Types

9 Chapter 169Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Name Service A multiagent architecture requires scalable, symbolic name resolution Alternative naming approaches FIPA LDAP Jini CORBA Naming Service JNDI

10 Chapter 1610Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

11 Chapter 1611Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Agent Framework Services (CoABS)

12 Chapter 1612Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

13 Chapter 1613Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns FIPA Agent Management System

14 Platform Services Chapter 1614Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

15 Chapter 1615Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

16 Standard Components of the FIPA Communication Model Chapter 1616Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

17 Chapter 1617Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Java Agent Development Framework JADE, the most popular, FIPA-compliant agent framework for multiagent systems: The most established of the publicly available agent frameworks FIPA-OS and Zeus having died

18 Chapter 1618Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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 backtracking TMSs are important because they deal with atomicity deal with the frame problem lead to efficient search

19 Chapter 1619Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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 Problem Solver TMS justifications beliefs

20 Chapter 1620Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

21 Chapter 1621Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

22 Chapter 1622Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

23 Chapter 1623Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Cooperative Service: 1 Client f3: afford(xcorp) IN r3: buy(X) :- query(Broker recommend(X)), afford(X) IN Broker f1: afford(xcorp) OUT f2: cash-rich(xcorp) IN r2: recommend(X) :- takeover-bid(X) IN r1: takeover-bid(X) :- cash-rich(X) IN ? recommend(?X)

24 Chapter 1624Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Cooperative Service: 2 Client f3: afford(xcorp) IN r3: buy(X) :- query(Broker recommend(X)), afford(X) IN Broker f1: afford(xcorp) OUT f2: cash-rich(xcorp) IN r1: recommend(X) :- takeover-bid(X) IN r2: takeover-bid(X) :- cash-rich(X) IN f3: recommend(xcorp) IN Shared with: Client; Justification: (f2 r1 r2) recommend(XCorp)

25 Chapter 1625Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Cooperative Service: 3 Client f3: afford(xcorp) IN r3: buy(X) :- query(Broker recommend(X)), afford(X) IN f4: recommend(xcorp) EXTERNAL Shared with: Broker; Justification: ( ) f5: buy(xcorp) IN Justification: (f3 f4 r3) Broker f1: afford(xcorp) OUT f2: cash-rich(xcorp) IN r1: recommend(X) :- takeover-bid(X) IN r2: takeover-bid(X) :- cash-rich(X) IN f3: recommend(xcorp) IN Shared with: Client; Justification: (f2 r1 r2)

26 Chapter 1626Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Cooperative Service: 4 Client f3: afford(xcorp) IN r3: buy(X) :- query(Broker recommend(X)), afford(X) IN f4: recommend(xcorp) EXTERNAL Shared with: Broker; Justification: ( ) f5: buy(xcorp) IN Justification: (f3 f4 r3) Broker f1: afford(xcorp) OUT f2: cash-rich(xcorp) IN --> OUT r1: recommend(X) :- takeover-bid(X) IN r2: takeover-bid(X) :- cash-rich(X) IN f3: recommend(xcorp) IN --> OUT Shared with: Client; Justification: (f2 r1 r2) relabel recommend(XCorp)

27 Chapter 1627Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Cooperative Service: 5 Client f3: afford(xcorp) IN r3: buy(X) :- query(Broker recommend(X)), afford(X) IN f4: recommend(xcorp) OUT Shared with: Broker; Justification: ( ) f5: buy(xcorp) OUT Justification: (f3 f4 r3) Broker f1: afford(xcorp) OUT f2: cash-rich(xcorp) OUT r1: recommend(X) :- takeover-bid(X) IN r2: takeover-bid(X) :- cash-rich(X) IN f3: recommend(xcorp) OUT Shared with: Client; Justification: (f2 r1 r2)

28 Chapter 1628Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

29 Chapter 1629Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

30 Chapter 1630Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Challenges Doing the "right" thing Autonomy Conventions: emergence and maintenance Coordination Collaboration Communication: semantics and pragmatics Interaction-oriented programming

31 Chapter 1631Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

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

33 Chapter 1733Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Highlights of this Section Contracts Spheres of Commitment Achieving Collaboration via Conventions Policies Negotiation

34 Chapter 1734Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

35 Chapter 1735Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

36 Chapter 1736Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

37 Chapter 1737Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Legal Abstractions Contracts Directed obligations Hohfeldian concepts Compliance

38 Chapter 1738Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

39 Chapter 1739Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

40 Chapter 1740Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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 …

41 Chapter 1741Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

42 Chapter 1742Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

43 Chapter 1743Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

44 Chapter 1744Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

45 Chapter 1745Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

46 Chapter 1746Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

47 Chapter 1747Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

48 - 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

49 Chapter 1749Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

50 Chapter 1750Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns A Selling VE (Composition Example)

51 Chapter 1751Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

52 Chapter 1752Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Teamwork When a team carries out some complex activity Negotiating what to do Monitoring actions jointly Supporting each other Repairing plans

53 Chapter 1753Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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)

54 Chapter 1754Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Negotiation Mechanism Attributes Efficiency Stability Simplicity Distribution Symmetry E.g., sharing book purchases, with cost decided by coin flip

55 Chapter 1755Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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??)

56 Chapter 1756Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

57 Chapter 1757Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

58 Chapter 1758Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Problem Domain Hierarchy Worth-Oriented Domains State-Oriented Domains Task-Oriented Domains

59 Chapter 1759Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Task-Oriented Domains: 1 A TOD is a tuple, 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

60 Chapter 1760Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Task-Oriented Domains: 2 A deal is a redistribution of tasks Utility of deal d for agent k is U k (d) = c(T k ) - c(d k ) 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

61 Chapter 1761Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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 deal This protocol is simple, symmetric, distributed, and guaranteed to end in a finite number of steps in any TOD. What strategy should an agent adopt?

62 Chapter 1762Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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)

63 Chapter 1763Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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) A1A2

64 Chapter 1764Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

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

66 Chapter 1866Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Highlights of this Section Agent Communication Languages Speech Act Theory Semantics Interaction Patterns Combining ACLs with Web Services Contract Net Protocol Business Protocols

67 Chapter 1867Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

68 Chapter 1868Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

69 Chapter 1869Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

70 Chapter 1870Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Speech Act Theory Communicative 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

71 Chapter 1871Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

72 Chapter 1872Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

73 Chapter 1873Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns FIPA FIPA is the Foundation for Intelligent Physical Agents, with website at Moved into IEEE Specifies standards for heterogeneous, interoperating agent-based systems Concerned with agency as it relates to Autonomous behavior Communication with other agents

74 Chapter 1874Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

75 Chapter 1875Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Low-Level Patterns

76 Chapter 1876Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Combining Agents with Traditional Web Services ACL is the FIPA ACL standard

77 Chapter 1877Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

78 Chapter 1878Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

79 Chapter 1879Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

80 Chapter 1880Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

81 Chapter 1881Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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)

82 Chapter 1882Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

83 Chapter 1883Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns NetBill Enhanced by CMs Meanings: 1. true 2. request 3. offer 4. C m goods  accept  promiseReceipt 5. goods  C c pay  promiseReceipt 6. goods  pay  C m receipt 7. goods  pay  receipt 8. goods  promiseReceipt 9. accept Final state: No open commitments remain

84 Chapter 1884Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Message Patterns for Commitment Operations Ensure that information about commitment operations flows to the right parties, to enable local decisions

85 Chapter 1885Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

86 Chapter 1886Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

87 Chapter 1887Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

88 Chapter 1888Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Fish-Market Sample Execution Based on a vector clock

89 Chapter 1889Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns Fish-Market Local Observations The discharge of a commitment must be reachable from its create

90 Chapter 1890Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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

91 Chapter 1891Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and 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


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