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Katia Sycara AAAI'97 1
James Bond and Michael Ovitz The Secret Life of Agents
Katia Sycara
The Robotics Institute
Carnegie Mellon University
Pittsburgh, PA 15213
(412) 268-8825
http://www.cs.cmu.edu/~sycara
Project Homepage: http://www.cs.cmu.edu/~softagents
Katia Sycara AAAI'97 2
Liren Chen
Somesh Jha
Rande Shern
Dajun Zeng
Keith Decker
Anadeep Pannu
Vandana Verma
Team Members CMU
Prasad Chalasani
Kostya Domashnev
Onn Shehory
Katia Sycara AAAI'97 3
Talk Outline
• Introduction to Agents
• Motivations and advantages of distributed agent technology
• The Retsina Approachª
• Retsina Agent Architecture
• Middle Agents
• Multi-agent interaction protocols (negotiation, contingent contracting)
• Retsina Applications
• Concluding Remarks
________________________________
ª Retsina stands for “Reusable Task Structured Intelligent Networked Agents.”
Katia Sycara AAAI'97 4
The (Re)-Emergence of Agents: The Marriage of Two Holy Grails
•Goal-directed•Adaptive•Knowledge-based
•Reusability•Robustness•Flexibility
AI SE
Ubiquitous Networked Information Access
Intelligent Software Agents!
Katia Sycara AAAI'97 5
What is an Agent?
• A computational system that
– has goals, sensors and effectors
– is autonomous
– is adaptive
– is long lived
– lives in a networked infrastructure
– interacts with other agents
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Agent vs. Agent
James Bond Michael Ovitz
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Next Generation of Agent Technology
• Currently, agent technology is mostly single agent focusing on information retrieval and filtering according to user profile
• Multi-Agent Systems that interact with humans and each other
• Integrate information management and decision support
• Enable real-time synchronization of the tasks and actions of humans in teams and organizations
• Acquire and disseminate timely and relevant information
• Anticipate and satisfy human information and problem solving needs
• Notify about changes in the environment
• Adapt to user, task and situation
Katia Sycara AAAI'97 8
Motivation for Multi Agent Systems (MAS) Technology
• Global Information & Markets
• Increasingly networked world
• Vast quantities of unorganized information
• Diverse information sources
• Inability for human to manage information access process---information overloading
• Moving from locating documents to making decisions
Katia Sycara AAAI'97 9
Features of MAS
• Multiple agents connected through communication networks
• Coordination - no agent has sufficient information or capabilities to solve problem aloneª
• Decentralized control - no master agent
• Decentralized data - no global data storage
• Agent Coupling - balancing computation and communication
• Asynchronous - multiple activities operating in parallel
_______________________
ª Agents could be cooperative or self-interested.
Katia Sycara AAAI'97 10
MAS Basic Questions (Bond and Gasser, 88)
• Coherence in coordinated decision making
• Recognition and reconciliation of disparate viewpoints or conflicting intentions
• Graceful performance degradation in face of missing information and resources
• Satisfaction of system-wide criteria (e.g., optimality of solution, hard real-time deadlines, etc.)
• How to recognize workload imbalances and appropriately redistribute activities and responsibilities among agents
• Modeling other agents
• Synthesizing different views and results
Katia Sycara AAAI'97 11
MAS Concepts and Tools
• Distributed Constraint Satisfaction and Optimization (Yokoo, et al,~1991; Sycara, et al. 1991)
• Distributed Truth Maintenance and Multi-Agent Search (Huhns et al. 1991, Ishida 1997)
• Organizational Structuring (Lesser and Corkill 1991, Gasser 1993, Decker 1995)
• Multiagent Planning (Georgeff 1983, 1984, 1995; Durfee and Lesser 1991, Jennings 1995, Grosz et al. 1996)
• Contracting (Smith 1980, Mueller 1993, Sandholm 1997)
• Negotiation (Sycara 1990; Kraus 1991, Zlotkin 1996)
Katia Sycara AAAI'97 12
MAS Concepts and Tools (Contd.)
• Economic and Game Theoretic Techniques (Rosenschein 1995; Gmytrasiewicz et al. 1991, Wellman 1993)
• Open systems (Hewitt 1991, Gasser 91)
• Multiagent Logics and Ecological Approaches (Cohen and Levesque 1987; Ferber 1990, Shoham 1993; Huberman et al. 1996)
• Social Laws and Norms (Tenenholtz 1991, Castelfranchi 1993)
• Multi-Agent Learning (Sen 1993, Durfee 1994, Sycara 1996)
Katia Sycara AAAI'97 13
Retsina Approach
• Architecture that includes data- and knowledge-bases and a distributed collection of intelligent agentsª
• Reusable and composable agent components (agent editor, agent operating system)
• Operates in an open world
– agents, network links, and information sources appear/disappear
– uncertainty
• Dynamic agent team formation on-demand
____________________________
ª K.Sycara, K.Decker, A.Pannu, M.Williamson, and D.Zeng. Distributed Intelligent Agents. IEEE Expert, Dec-96
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Retsina Functional Organization
Katia Sycara AAAI'97 15
Main System Issues in MAS
• Single agent architecture
– Retsina agent architecture
– Agent Self-cloning
• Finding other agents
– Middle agents
– Matchmaking and brokering
• Agent interaction protocols
– Negotiation
– Contingent contracting
Katia Sycara AAAI'97 16
Retsina Agent Architecture
• Planning
– hierarchical task network-based formalism
– library of task reduction schemas
alternative task reductions
contingent plans, loops
– incremental task reduction, interleaved with execution
information gathered during execution directs future planning
• Scheduling
– fully expanded leaf nodes = executable basic actions
– enabled actions (all parameters and provisions in place)
– adjust periodic tasks with missed deadlines
Katia Sycara AAAI'97 17
•Communication and Coordination
–processes incoming and outgoing messages
–creates new goals/objectives
–determines coordination interactions
–addresses security issues
•Execution Monitoring
•setup execution context (parameters and provisions)
•action monitoring
deadlines/timeouts
data collection for decisions (e.g. cloning)
•complete execution (provide results to appropriate downstream actions)
Katia Sycara AAAI'97 18
Retsina Agent Architecture
Katia Sycara AAAI'97 19
A task Structure (Advertisement Task Structure)
Katia Sycara AAAI'97 20
Reusable Behaviors
• Advertising
– send agent capability model to middle-agent(s)
– shared query behavior for other agents
• Polling for messages
• Answering queries: one-shot and periodic
• Monitoring for changes and notification
• Self-cloning
Katia Sycara AAAI'97 21
Self-Cloning Process
• Agents that perceive an overload look for other agents to pass tasks to (simple model to predict idle time using learned estimation of task durations)
• When other agents not found:
– locate a host with resources for cloning
– create a clone on the host
– partition tasks and transfer to clone
– the ``old'' agent updates its advertisement; the ``clone'' agent advertises
• When clone is idle -- consider self-extinction, and shut down if necessary.
Katia Sycara AAAI'97 22
Cloning Experimental Setting
• Number of agents: 10 to 20.
• Number of clones allowed: up to 10.
• Number of tasks arriving at the system: up to 1000.
• Task distribution with respect to the required capabilities for execution: normal distribution, where 10% of the tasks are beyond the capabilities of the agents.
• Agent capabilities: an agent can perform up to 20 average tasks
simultaneously.
Katia Sycara AAAI'97 23
Task Completion w/wo Cloning
Katia Sycara AAAI'97 24
Middle Agents
• An agent needs to have some task/service performed. How can it find agents able to perform that task?
• In an open system:
– agents generally don't have knowledge of all other agents
– service providers are liable to come and go over time
• A solution: middle agents that specialize in making connections between agentsª
_________________________
ª K.Decker, K.Sycara, M. Williamson. Middle-Agents for the Internet. IJCAI-97
Katia Sycara AAAI'97 25
Middle Agent Types
PreferencesInitially Known By
Provider Only Provider +Middle Agent
Provider + Middle +Requester
Requester Only (Broadcaster) “Front-Agent” Matchmaker/Yellowpages
Requester +Middle Agent
Anonymizer Broker Recommender
Requestor +Middle + Provider
Blackboard Introducer/Bodyguard
Arbitrator
Capabilities Initially Known By
Katia Sycara AAAI'97 26
Matchmaking: Agent Yellow Page Services
Katia Sycara AAAI'97 27
Matchmaking in Agent Coordination
• When an agent A advertises its capability, it Intends toª perform any task that fits the specification of that capability.
– In the Retsina system an agent A advertises a relational schema SA, i.e., agent A intends to answer any query on its schema.
• If an agent B finds another agent A with a certain capability through matchmaking, B believes that agent A can successfully perform the task.
• Matchmaking gives operational semantics to predicates such as Intend.to, Bel.
_______________________________
ª Grosz and Kraus 1996
Katia Sycara AAAI'97 28
Performance of Match-made System
Katia Sycara AAAI'97 29
Performance of Brokered System
Katia Sycara AAAI'97 30
Agents in Electronic Commerce
Katia Sycara AAAI'97 31
Adaptive Negotiation (the Bazaar Model)
• Aims at modeling multi-issue negotiation processesª
• Combines the strategic modeling aspects of game-theoretic models and single agent sequential decision making models
• Supports an open world model
• Addresses heterogeneous multi-agent learning utilizing the iterative nature of sequential decision making and the explicit
representation of beliefs about other agents ______________________________
ª D.Zeng and K.Sycara. “Benefits of Learning in Negotiation.” Proceedings of AAAI-97.
Katia Sycara AAAI'97 32
Utility of Learning: Experimental Design
• The set of players N is comprised of one buyer and one supplier who make alternative proposals.
• For simplicity, the range of possible prices is from 0 to 100 units and this is public information
• The set of possible actions (proposed prices by either the buyer or the supplier) A equals to {0, 1, 2,…, 100}
• Reservation prices are private information.
• Each player's utility is linear to the final price ( a number between 0 and 100) accepted by both players
• Normalized Nash product as joint utility (the optimal joint utility
when full information is available is 0.25)
Katia Sycara AAAI'97 33
Average Performance of Three Experimental Configurations in Bazaar
• A non-learning agent makes decisions based solely on his own reservation price
• A learning agents makes decisions based on both the agent's own and the opponent's reservation price
Configuration JointUtility
Buyer’sUtility
Supplier’s Utility
# of ProposalsExchanged
Both Learn 0.22 0.49 .051 24
Neither Learn 0.18 0.49 0.51 34
Only Buyer Learns 0.15 0.59 0.41 28
Katia Sycara AAAI'97 34
Contingent Contracts and Options
• Most multi-agent systems don't handle uncertainty effectively
– rigid task delegation mechanism (contracts are binding rather than contingent
– no explicit modeling of stochastic events
– no explicit mechanism for controlling agent performance variability
• We are exploring the use of option pricing to address the above issues
Katia Sycara AAAI'97 35
Evaluation of Contingent vs Binding Contracts
• In the experiments, we only had two kinds of agents:
– Interface Agents: Accept queries from the user.
– Information Agents: Answer queries given by the Interface agents.
• In each cycle a new information agent with a load randomly distributed
between L and 0.9 appears with probability .
• When a new information agent comes up, interface agents have the option to abort the query on the old information agent and restart it on the new one.
• Interface agents can only switch a bounded number of queries to the new agent. This is indicated as Bound in the graphs.
• In the experiments the average delay in answering the queries was measured. This is indicated as Delay in the graphs.
Katia Sycara AAAI'97 36
Contingent Contracts
L
Katia Sycara AAAI'97 37
Contingent Contracts
Bound
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Contingent Contracting to Handle Unreliability of Information Sources
• Uncertain waiting time in response to queries
– random network congestion
– uncertain serve congestion/breakdown
Katia Sycara AAAI'97 39
The Query Restart Problem
• Agent A sends query to Agent B.
• Agent B can complete the query in time X, where
X = 1 with probability p.
X = c (c > 1) with probability 1 - p.
Expectation: EX = p + (1 - p) c
• If not done by time 1, should agent A abort and restart, or wait?
• Can restarting reduce expectation? The variance? Both?
• Does it help to repeatedly restart k times?
Katia Sycara AAAI'97 40
Strategy: restart just after time 1, if not done by then.
Let Xi = completion time of i'th query, i = 1,2.
X1, X2 are independent, identically distributed.
New completion time is Y:
Y =
New expectation
EY = p + (1 - p)(1 + E X2) (X1, X2 indep.)
= 1 + p (1 - p) + (1 - p) c
If (and only if) c > 1 + 1 / p, EY < X1 !
A Simple Scenario: Single restart
{ 1 if X1 = 1,
1 + X2 if X1 = c.
Katia Sycara AAAI'97 41
A Simple Scenario: k Restarts
Number of Restarts k
Katia Sycara AAAI'97 42
Applications
• Visitor Hoster (PLEIADES)
• Satellite Visibility (THALES)
• Portfolio Management (WARREN)
Katia Sycara AAAI'97 43
Characteristics of Retsina
• Open System
• Adaptivity at the agent and organization level provides robustness
• Service-based, economic coordination of agents
• Reusable and extensible domain-independent computational infrastructure
• Integrates information gathering and execution monitoring with decision making
• Framework for addressing uncertainty and strategic
interactions
Katia Sycara AAAI'97 44
Future of Software Agents• Agent-based software development is an emerging paradigm
• Agent society that parallels human society
• Implication of the emergence of agent society for human workplaces, institutions, and social relations
• Agent society as a unit of intelligence
• Opportunities and Challenges
– The WEB is a vast knowledge base presenting novel opportunities for AI
– Overall system (human and software agent) predictability
– Security, privacy, trust issues
– Integration of legacy systems
Katia Sycara AAAI'97 45
Overall Issues in Open MAS
• Overall agent organization
• Single agent architecture
– Retsina agent architecture
Agent Self-cloning
• Finding other agents
– Middle agents
Matchmaking and brokering
• Agent interaction protocols
– Negotiation
– Contingent contracting
Katia Sycara AAAI'97 46
Overall Issues in Open MAS
• Overall agent organization
• Single agent architecture
– Retsina agent architecture
Agent Self-cloning
• Finding other agents
– Middle agents
Matchmaking and brokering
• Agent interaction protocols
– Negotiation
– Contingent contracting
Katia Sycara AAAI'97 47
Overall Issues in Open MAS
• Overall agent organization
• Single agent architecture
– Retsina agent architecture
Agent Self-cloning
• Finding other agents
– Middle agents
Matchmaking and brokering
• Agent interaction protocols
– Negotiation
– Contingent contracting