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Welcome. Welcome to the Dagstuhl seminar on Plan Recognition Please upload titles for the talks you want to give We would like everyone to have an opportunity to give a short talk We have some panel ideas, but these are open to reconsideration – contact me - PowerPoint PPT Presentation
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Welcome Welcome to the Dagstuhl seminar on Plan
Recognition Please upload titles for the talks you want to
give We would like everyone to have an opportunity to give
a short talk We have some panel ideas, but these are open
to reconsideration – contact me We will be scheduling incrementally
Scheduled through tomorrow… Schedules will be re-posted as updated… 1
Panel ideas Should there be a plan recognition
competition? Rational versus fallible agents Activity recognition, behavior recognition,
plan recognition, goal recognition Oh, my!
Full and partial observability Generative versus plan library approaches
2
Schedule: Monday AM: Welcome and survey PM:
Jerry Hobbs: discourse and plan recognition Short talks
George Ferguson Matthew Stone
Chris Baker: plan recognition and psychology Panel: a plan recognition competition?
Evening: get acquainted event3
Schedule: Tuesday AM:
Kathy Laskey: probabilistic methods for PR Short talks
Froduald Kabanza Francis Bisson Gita Sukthankar
PM: Tom Dietterich: learning and plan recognition Short talks
David Pattison Nate Blaylock
Panel: Rational versus fallible agents? 4
Plan RecognitionHistorical Survey
Henry KautzUniversity of Rochester
Robert P. GoldmanSIFT, LLC
Dagstuhl, April 20115
Old school plan recognition…
Outline Dimensions of the plan recognition problem Historical survey of methods Challenges
6
DIMENSIONS OF PLAN RECOGNITION
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Keyhole, intended and adversarial plan recognition Keyhole
Observer non-intrusively watches the agent Determine how an agent’s actions contribute to
achieving possible or stipulated goals Model
World Agent’s beliefs
8
Keyhole, intended and adversarial plan recognition Intended recognition
Agent acts in order to signal his beliefs and desires to other agents Speech acts – inform, request, …
Discourse conventions “The 3:15 train to Windsor?” “Gate 10” [Allen & Perrault]
Symbolic actions The Statue of Liberty 9/11?
The agent may require a model of the observer.9
Keyhole, intended and adversarial plan recognition Adversarial
Agent acts in order manipulate the observer Deception, bluffing, misdirection, etc. …
Agent and observer will need sophisticated models of each other’s inferences
10
Ideal versus fallible agents Mistaken beliefs
John drives to Reagan, but flight leaves from Dulles.
The doctor bleeds the patient to cure disease. Cognitive errors
Distracted by the radio, John drives past the exit. Jill schedules a doctor’s appointment during her
office hours. Irrationality
John furiously blows his horn at the car in front of him.
11
Output of plan recognition Activity recognition
Simply identify a known behavior pattern Goals
Recognize the objective, but not the specific recipes used
Plans Next action the agent will take? Best action to aid or counter the agent?
12
Output of plan recognition: likelihood Likelihood…
Most likely interpretation? Distribution over plans and goals? The above have subtly different strengths and
weaknesses… Most critical plan or goal?
13
Richness of plans Are actions atomic?
Or do they have parameters? Structure (e.g., cases)?
Do plans have structure and parameters? Coreference? The patient of the plan will be the destination of
step one and the patient of step two… Are there plan libraries at all?
14
Other dimensions Reliable versus unreliable observations
“There’s a 80% chance John drove to Dulles.” Open versus closed worlds
Fixed plan library? Fixed set of goals? Fixed set of entities?
Metric versus non-metric time John enters a restaurant and leaves 1 hour later. John enters a restaurant and leaves 5 minutes later.
Single versus multiple ongoing plans “White knights”
Static versus evolving set of intentions Abandoning goals: I was going to drive to the store, but the weather was
too bad. Reacting to opportunities: I was going by the playroom on the way from
the laundry, so I picked up the toys.15
Dimensions
Relation to agent
Model of agent
Goals and plans
Observ-ations
Infer Model (library)
Produce
Intended (possibly) Irrational
Static Noisy Activity Incomplete “The Answer”
Keyhole Partial knowledge
Partial Goal Best answer
Adversar-ial
Homo Econom-icus
Dynamic Complete Plan Complete Distribu-tion
Next action
16
METHODS
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Earliest work Generally in service of language
understanding Often narrative understanding Understanding indirect speech acts
Allen & Perrault, “Analyzing Intention in Utterances,” AI, 1980
Rich vein of work using plan recognition in dialog understanding and IUI Will be hearing more from George Ferguson later today!
Methodologically: Mostly shared early enthusiasm for rule-based systems 18
Hypothesize & Revise
The Plan Recognition Problem C. Schmidt, 1978 Related work from Yale AI Lab: Cullingford’s Script
Applier Mechanism, Wilensky’s PAM, etc., 1978 Charniak, Ms. Malaprop, 1978 – Frame-based and
used TMS
Based on psychological theories of human narrative understandingMention of objects suggest hypothesisPursue single hypothesis until matching fails
19
Closed-world reasoning
A Formal Theory of Plan Recognition and its Implementation Henry Kautz, 1991
• Infers the minimum set(s) of independent plans that entail the observations
• Observations may be incomplete
• Infallible agent• Complete plan
library• Limited to pasta
preparation
20
Parsing Vilain 1990 --- use parsing results to characterize
computational complexity of plan recognition There were earlier attempts to parse plans
Parsing techniques closely related to Closed-world reasoning (Built on Kautz and Allen) Find an explanation that covers all of the observations Parsing techniques deal poorly with partial ordering,
worse with interleaving Leads to:
Later work on stochastic parsing (Pynadath and Wellman) Attempts to exploit exotic parsing techniques (Geib)
21
Abduction Reason from effect to cause (C.S. Peirce)
Explanation Diagnosis
People: Charniak Hobbs et al., TACITUS
Leads to interest in Bayes nets
22
Bayes Nets DAG-structured
models of probability distributions
Came into the fore for diagnostic applications
Challenge: Static Bayes nets for complex domains can be extremely large
SprinklerRaining
Grasswet
23
Bayes Nets Knowledge Based
Model Construction: Dynamically build Bayes nets showing how plans explain actions
Multiple goals Abstraction
hierarchies Equality reasoning for
coreference Poor treatment of
time
• “A Bayesian Theory of Plan Recognition,” Charniak and Goldman, AIJ, 1993.• “Interpretation as Abduction,” Hobbs, Stickel, Martin & Edwards, Proc. ACL,
1988.
“Jack went to the liquor store.”Was he shopping?
24
More on Bayes net methods Laskey and her colleagues have worked on
military domains Further developed KBMC techniques (e.g. query
completeness); coreference, identity uncertainty Many related techniques
E.g., Hobbs et al. cost-based abduction ATMSes (d’Ambrosio, Provan, Charniak &
Goldman) Horn logic (Poole)
25
Pending sets
A new model of plan recognition. Goldman, Geib, and Miller,1999“A probabilistic plan recognition algorithm based on plan tree grammars,”
Geib and Goldman, AIJ, 2009.
Explicitly models the agent’s “plan agenda” using Poole’s “probabilistic Horn abduction” rulesBridge between Bayes net and HMM frameworksHandles multiple concurrent interleaved plans & negative evidenceNumber of different possible pending sets can grow exponentially
Happen(X,T+1) Pending(P,T), X in P, Pick(X,P,T+1).
Pending(P’,T+1) Pending(P,T), Leaves(L), Progress(L, P, P’, T+1).
26
Version Space Algebra
A sound and fast goal recognizer Lesh & Etzioni, IJCAI 1995 Programming by Demonstration Using Version Space Algebra Lau,
Wolfman, Domingos, Weld. Related to later work on plan-recognition through planning
• Recognizes novel plans
• Complete observations
27
CHALLENGES
28
Evaluation Ground truth
Difficult to get labeled data Epistemic question --- do our proposed labelings
correspond to any real ground truth? Prediction tasks
Next action? Future action? Good choice of assistive action?
Countermeasure? Can prediction act as proxy for ground truth?
29
Epistemic question What is the status of the recipes that we
postulate as explanations for actions? Are they taken as being real in some sense?
Corresponding to mental contents? Identified regularities that really exist in the world? Data structures that just exist for our convenience
30
Computational difficulties Computational complexity
Theoretical results Practical results Challenges from domains
Some domains inherently ambiguous Adversarial reasoning Do we need game-theoretic reasoning
Cooperative as well as adversarial
31
Plan libraries Engineered? Learned? Something in between?
Learned ones often seem impoverished Engineering seems impossible!
32
Learning Structural learning
Learn the contents of plan libraries (in one form or another)
Parameter learning Adjust parameters of known libraries
Both offer challenges related to those of evaluation
Plan recognition may be done in service of learning, as well as the other way around. Infer goals to learn novel recipes 33
Imperfections Imperfect agents
Imperfect information Imperfect reasoning Imperfect task performance Challenging for non-empirical algorithms
Imperfect observations Imperfect models
Including seemingly-irrelevant actions
34
User models In many domains, the behaviors exhibited are
not just a function of the actions, goals and plans, but agent characteristics, as well.
Developing clean ways to combine agent-dependent and – independent information is a challenge going forward. Often per-agent training is unacceptable.
35
Sensing In many cases it is difficult to sense the agents’
actions: Labeling actions in primitive sensor data
Vision Network packets Linguistic utterances
Hardware/software hybrid systems E.g., oil refinery --- user can go out and use a wrench un-
observed Conventional software
Even Horvitz et al. report difficulties “seeing” actions of Microsoft Office users
Mixed streams Individual actions in network packet streams
36
Coreference and quantification In some domains we don’t have object
identity and permanence and the number of agents simply handed to us. Story understanding Military situation interpretation
Identity hypotheses enter into plan recognition
37
Anomaly detection Often appealed to as a solution for detecting
some phenomenon that is difficult to model: Intrusion behavior in computer security Terrorist behavior in tracking and camera data Dementia-induced behavior in tracking elderly
subjects Accuracy requires deep understanding of the
models’ properties Stationarity (often violated in computer security) “Size” and “shape” of normal behaviors
As always, it’s hard to get something for nothing.38
The Role of State Many (but not all) plan recognition systems
represent only the state of the planning agent. The state of the environment is modeled implicitly,
if at all.
39
Groups Teamwork
Friendly: recognize teammates’ intentions to coordinate and aid
Hostile: recognize opponents’ intentions to hinder and obstruct
Role recognition
40
Hypothesis retrieval Some early work assumed that there were
enough candidate hypotheses that retrieval could be an issue
41
Predictive and explanatory inference A lot of concern in early work about
combining top-down and bottom-up inference
42
Actions with weak diagnostic power E.g., computer security We would desperately like to know the
attacker’s motivations But what do we do with
Get access to the target Gain administrator privileges on the target…
43
COFFEE AND THEN HENRY’S TURN…
44