1 of 20 23rd annual workshop on qualitative reasoning (qr 2009) ljubljana, slovenia, june 22 - 24,...

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23rd Annual Workshop on Qualitative Reasoning (QR 2009) Ljubljana, Slovenia,June 22 - 24 , 2009

Model Building Experiences using Garp3: Problems, Patterns and

Debugging

Jochem Liem, Floris E. Linnebank & Bert BredewegHuman-Computer StudiesUniversity of Amsterdam

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Motivation: Usability to Formalization Bottleneck• Availability of usable QR tools has led to:– More domain experts formalizing their conceptual

knowledge– The creation of more complex models

• Usability is no longer an issue• However, knowledge formalization is the new

bottleneck• Modelers encounter similar representational

issues, and reinvent solutions • This paper categorizes representation issues and

their solutions.

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Trained Groups in QR Modelling• PhD-level researchers (NaturNet-Redime)– 2,5 year working with Garp3– Trainings each half year– Support using Skype/Flashmeeting

• BSc. Students (Future Planet Studies)– 4 weeks: Concept maps, Ontologies– 4 week: QR modelling (Carbon Cycle)

• PhD-students (School for Information and Knowledge Systems)– 1 hour lecture + 2 hour practical: Tree & Shade model

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Entities or Quantities?

• Alternative representations:– Algae entity with Biomass

quantity– Algea concentration quantity

• Create a new entity when properties of this entity are important.

• E.g. photosynthesis quantity of the algae

Model by Elena Nakova , Yordan Uzunov

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Configuration direction & naming

• Model by Richard Noble, Floris E. Linnebank & Bert Bredeweg

• Prefer active voice over passive voice• Shorter configuration names• Improves texts based on QR models

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Relation reification

• Configuration direction is arbitrary• Long configuration name• Where to model speed of symbiosis process?

• Model by Paulo Salles & Bert Bredeweg

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Influences & Proportionalities

Q1[+,-] Q2[+,?]I+

Q1[+,-] Q2[+,?]I-

Q1[-,-] Q2[+,?]I+

Q1[-,0] Q2[+,?]I-

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Causal Interactions

Q1[+,-] Q2[+,?]I+

Q1[+,-] Q2[+,?]I-

Q1[-,-] Q2[+,?]I+

Q1[-,0] Q2[+,?]I-

Q3[-,-]I+

Q3[-,-]I+

Q3[-,-]I-

Q3[-,-]I-

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Causal Chains

• Causal path: Influence followed by proportionalities• Rare: Multiple influences in a single causal path• Impossible: Loop of proportionalities

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Multiple Competing Influences• CO2 release I+ CO2 Concentration • Burning I+ Co2 Concentration• Inequality information does not help

• Burning + CO2 concentration > 0• Introduce Photosynthesis• Burning + CO2 < Photosynthesis

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Choosing Quantity Spaces• Difficult task even for expert modelers• Should be behaviorally significant• Depends depends on the context: – Phytoplankton blocking sunlight of 1st producers– Global warming’s effect on phytoplankton

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{Small, Medium, High} considered harmful

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Actuators: External actuator (1/3)

• Models (effect of) process outside the system– Value assignment (MF)

– Exogenous behaviour (Scenario)

• Model by Eugenia Cioaca, Tim Nuttle, Bert Bredeweg

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Actuators: Equilibrium Seeking Mechanism (2/3)

• Models equalizing flows due to potential difference

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Actuators: Competing Processes Pattern (3/3)

• Models competing processes

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States in simulation• Maximum number of states:– Cartesian product of all quantities– E.g. Three Q’s: (3x3)3=729 (excl. inequalities)

• Successor states without correspondences:– S-states = 2q-1, q = non-corresponding quantities

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Not all expected states• Issue: State is missing• Create the state as a scenario– Option 1: No states, state is inconsistent– Option 2: State appears

• Next create a scenario that generates a previous state

• Continue to a state in the original simulation

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No States• Considered difficult to debug• Features:– Inconsistency– > 1 model fragment fired– Clash between contents of:

• Scenario + MF • Multiple MFs

• Troubleshooting:– Deactivate all MFs (at least 1 state from scenario)– Activate MFs one by one

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Inconsistencies

• Magnitude or derivative value assignments (MF or scenario)

• Inequalities (MF or Scenario)

• Operators (plus or minus)

• Value assignments due to correspondences

• Value assignments due to influence resolution

• Exogenous behavior• Engine rules• Quantity constraints• Continuity constraints

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Conclusions & Future Work• Catalog of – Representational issues and their solutions– Frequently occurring patterns – Considerations when debugging

• Future work: Support in Garp3/DynaLearn– Premade patterns (QS’s and actuators)– Automatic model building– Model diagnosis

1 of 20 23rd annual workshop on qualitative reasoning (qr 2009) ljubljana, slovenia, june 22 - 24,...

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