Cerutti--AAAI Fall Symposia 2009

University of BresciaDipartimento di Elettronica per l'Automazione

Knowledge Engineering and Human-Computer Interaction Research Group

© 2009 Federico Cerutti <[email protected]>

An Argumentation-based An Argumentation-based Approach to Modelling Decision Approach to Modelling Decision Support Contexts with What-If Support Contexts with What-If

CapabilitiesCapabilities

Pietro Baroni, Federico Cerutti, Massimiliano Giacomin and Giovanni GuidaPietro Baroni, Federico Cerutti, Massimiliano Giacomin and Giovanni Guida

AAAI 2009 Fall Symposium SeriesThe Uses of Computational Argumentation

Arlington, November, 5, 2009


“Good advice”

The advice should be presented in a form which can be readily understood by decision makers

There should be ready access to both information and reasoning underpinning the advice

If decision support involves details which are unusual to the decision maker, it is of primary importance that s/he can discuss these details with his advisor

Girle et al., 2003


Transparency about the advice

Practical reasoningabout “what to do”

Knowledgerepresentation

Computation ofoutcomes


Knowledge representationKnowledge representation➢ Computation of outcomes

➢ Conclusions and future works


Argument (and attack) schemes

Use of argument scheme to represent the knowledge Structure which contains the information in favour of

a given conclusion

Introduction of a possible modelling of conflicts by “attack scheme”

Structure which contains the information in favour of a given conflict


The main concepts

Circumstance: a state of the world Fact: a particular circumstance assumed to be true Goal: a state of the world we want to achieve Action: support for the achievement of a goal Preference: “[…] a greater liking for one alternative

over another or others […]” Value: “Worth or worthiness […] in respect of rank

or personal qualities” Must Value: a value that we commit to promote


Example (1)

Treatment for a patient threatened by blood clotting Goal: obtaining a low platelet adhesion The available knowledge base concerning

treatments: Administer Aspirin (value of Safety) Administer Chlopidogrel (value of Safety) Do nothing (value of Cost)


PAS: A2Circumstances: given patient's situationAction: we should administer aspirinGoal: reducing blood clottingValue: SafetySign: +

Formal counterpart (1)Practical Args (from Atkinson et al.)


Formal counterpart (1)The Attacks among PAS

PAtS1: αSource: A1Target: A2Conditions:A1.action and A2.action are incompatible


VAS: V1Value: Cost

Formal counterpart (1)The Values


Formal counterpart (1)The Defences from the Values

VDeS1: βSource: V2Target: αConditions:α.target.value = V2.value, α.source.value ≠ V2.value

PAtS1: α…




VDeS2: γSource: V1Target: βConditions:β.source ≠ V1, β.target.source.value ≠ V1.value

PAtS1: α…




VDeS2: γSource: V1Target: βConditions:β.source ≠ V1, β.target.source.value ≠ V1.valueVDefence: β

Defending: A2Defended: V2

VDefence: γDefending: A1Defended: V1

PAtS1: α…


Example (2)

From patient's file we learn that he has a history of gastritis

Then we should not administer Aspirin without a proton pump inhibitor

In fact, it gives rise to risk of ulceration And it will demote the value of Safety As far as we know, no proton pump inhibitor is

available


Formal counterpart (2)A PAS with negative sign...

PAS: A4Circumstances: proton pump unavailableAction: we should not administer aspirinGoal: risk of ulcerationValue: SafetySign: -


Formal counterpart (2)...and the relative attacks

PAtS2: δSource: A4Target: A2Conditions:A4.action = ¬ A2.action


Formal counterpart (2)...and the relative attacks

VAAtS: εSource: A4Target: βConditions: A4.circumstance = β.defended.circumstance, A4.action = ¬ β.defended.action, A4.goal = β.defended.goal, A4.value = β.defended.value, A4.sign = -, β.defended.sign = +

PAtS2: δSource: A4Target: A2Conditions:A4.action = ¬ A2.action


Example (3)

Suppose now that the assumption that no proton pump inhibitor is available reveals to be false

Suppose also that between aspirin and chlopidogrel a doctor prefers to administer aspirin because it is in stock and immediately available


FAS: A5Circumstances: a proton pump is available

Formal counterpart (3)A Fact


Formal counterpart (3)An “undercut”

FAtS: ζSource: A5Target: A4Conditions: A5.circumstances= ¬ A4.circumstances


PRAS: P1Preferred: A2Notpreferred: A3

Formal counterpart (3)A preference


Formal counterpart (3)The greater liking

PAtS: η...

FAtS: θSource: P1Target: ηConditions: P1.preferred = η.target, P1.notpreferred = η.source


Example (4)

Determine the ultimate decision outcome Achieve the goal of reducing blood clotting It promotes the value of Safety We must promote the value of Safety


MAS: MV2Value: Safety

Formal counterpart (4)The Must Value


Formal counterpart (4)What-If Scenario

MAtS2: κSource: MV2Target: γConditions: MV2.value = γ.target.source.value,MV2.value ≠ γ.source.value

VDeS2: γ...


Small SummaryArgument Scheme Taxonomy

Practical Argument Scheme Factual Argument Scheme Value Argument Scheme Preference Argument Scheme Must Argument Scheme


In the example


Small SummaryAttack Scheme Taxonomy (1)

PAtS1: incompatible actions PAtS2: “rebuttal” VAtS : incompatible values VDefence (VDeS[1-2]): a value protects both the

arguments which promote it and the attacks sourced from that arguments

VAAtS: if a practical argument P suggests not to perform an action A since it demotes a value V, if P will be considered acceptable, then V cannot defend the argument whose action is A


In the example (1)


Small SummaryAttack Scheme Taxonomy (2)

FAtS: “undercut” PRAtS: someone told us that an attack cannot be

considered since an external preference MAtS1: an instance of Must Argument Scheme has

to protect the related Value argument against the incompatible values

MAtS2: an instance of Must Argument Scheme has to protect the instances of VDefence which start from the related Value argument


In the example (2)


Computation of outcomesComputation of outcomes➢ Knowledge representation

➢ Conclusions and future works


Argumentation Framework for Decision Support Problem


Argumentation Framework withRecoursive Attacks (AFRA)


From AFDSP to AFRA


AFRA: Defeat relation


AFRA: Admissibility


AFRA: Preferred Extension


Recalling the example...


...and the preferred extension


Conclusions and Conclusions and future worksfuture works

➢ Knowledge representation➢ Computation of outcomes


Conclusions

Preliminary investigation about formalisation of decision support problems

Three main contributions: The role of attack schemes Attacks to attacks in practice Support to “What-if” reasoning


Future works

Knowledge representation: Enhancing attacks schemes Ontological status of attacks Multiple What-if Situations

Computation of outcomes Further investigation on the theoretical bases of AFRA Argumentation semantics in this context


Open questions

The notion of attack scheme: soundness and usefulness

Attack schemes and critical questions What-if only w.r.t. Values

Cerutti--AAAI Fall Symposia 2009

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