AOSE-2003, Melbourne July 15th 1

Agent Oriented modeling by interleaving formal and informal

analysis

Anna Perini1, Marco Pistore2,1, Marco Roveri1, Angelo Susi1

1ITC - IRSTVia Sommarive, 18, I-38050, Trento-Povo, Italy

{perini,roveri,susi}@irst.itc.it

2DIT, University of TrentoVia Sommarive, 14, I-38050, Trento-Povo, Italy

pistore@dit.unitn.it

AOSE-2003, Melbourne July 15th 2

Introduction

• What– Exploitation of Formal Techniques to guide and support

the analyst while building and refining Conceptual Models• Why

– Visual conceptual modeling is a core process in software development (RUP / AGILE)

» Weakness: lack of a formal semantics– Formal specifications languages provide a precise

semantics » Weakness: require strong skills, often ineffective for

discussing with the stakeholders

• How– Defining a framework which uses diagrammatic models

equipped with formal semantics» Agent Oriented approach (TROPOS)» Focus on Requisites specification

AOSE-2003, Melbourne July 15th 3

Outline

• Introduction

• Tropos by Example

– Informal modeling via Informal Tropos– Formal modeling via Formal Tropos

• The framework– Model assessment and refinement– Model validation– Model evolution

• Conclusions & Future Work

AOSE-2003, Melbourne July 15th 4

AO Visual Modeling with Tropos

Early RequirementsEarly Requirements Late RequirementLate Requirement Architectural DesignArchitectural Design

Software development activities

Actors in the organizational setting

System Actor Sub-system Actors

AOSE-2003, Melbourne July 15th 5

The example: Informal modeling

MethodologyProvides threeGoal analysisTechniques:

• AND/OR decomp.• Means-end analysis• Contribution

AOSE-2003, Melbourne July 15th 6

Informal Analysis via Tropos

• Benefits– Language ontology based on common sense (informal)

components (actors, goals, dependencies …)– A graphical notation– Reasoning mechanisms: AND/OR goal decomposition,

means-end analysis, goal contribution analysis, that allow to model the “why” domain and system requirements

• Weaknesses– Static view of the model (no dynamics for the generation

and achievement of goals, needs, dependencies …)– No temporal constraints (e.g., on the fulfillment of goals

and dependencies)

AOSE-2003, Melbourne July 15th 7

The Example: Formal modeling

Actor AdvisorActor ProducerGoal ManagePheromoneTrapPlant……Goal Area Collection

Actor AdvisorMode achieveAttribute mptp : ManagePheromoneTrapPlantCreation Condition not Fulfilled(mptp)Fulfillment condition

pp : PlantPlan (pp.actor=actor & Fulfilled(pp)) & …

……Goal Dependency OrchardsData……

• A Formal Tropos specification consists of a sequence of class declarations such as actors, goals and dependencies, that represents the formal counterpart of the objects in the informal specification

• Extends a Tropos specification with annotations that characterize the valid behaviors of the model

AOSE-2003, Melbourne July 15th 8

The Example: Formal modeling

Actor AdvisorActor ProducerGoal ManagePheromoneTrapPlant……Goal Area Collection

Actor AdvisorMode achieveAttribute mptp : ManagePheromoneTrapPlantCreation Condition not Fulfilled(mptp)Fulfillment condition

pp : PlantPlan (pp.actor=actor & Fulfilled(pp)) & …

……Goal Dependency OrchardsData……

• A Formal Tropos specification consists of a sequence of class declarations such as actors, goals and dependencies, that represents the formal counterpart of the objects in the informal specification

• Extends a Tropos specification with annotations that characterize the valid behaviors of the model

AOSE-2003, Melbourne July 15th 9

Formal Analysis via Tropos

• Benefits– The introduction of the temporal dimension in Tropos

Representation allow to produce scenarios to be validated by the stakeholders

– Domain representation can be Formally Verified (proof, counterexamples to correct the domain specification)

• Weaknesses– Formal languages are expressive but yet hard to be

understood (temporal constraints are expressed via a typed first-order linear time temporal logic LTL)

– Formal Results are hard to interpret in the informal setting

AOSE-2003, Melbourne July 15th 10

• We propose a framework based on the idea of exploiting formal techniques to guide and support the analyst while building and refining a conceptual model

• The framework has to support:• Model assessment and refinement, against

possible inadequacies • Model validation, with the stakeholders, to end up

with an agreed set of requirements• Model evolution, maintaining its consistency,

propagating changes, merging redundant information

• The framework will include a tool for:• an automatic translation from Informal to Formal• visualization of the query results

The framework

AOSE-2003, Melbourne July 15th 11

The Informal Analyst assesses the model against possible inconsistencies or redundancies or critical elements and eventually refines the informal model on the basis of the new answer of the Formal Analyst to his/her question

Model Assessment & Refinement

AOSE-2003, Melbourne July 15th 12

Model Assessment & Refinement (2)

• Is It possible for the Advisor to perform historical data analysis ?

FULFILLABLE HistoricalDataAnalysis

Manage Pheromone trap plant

HistoricalData

analysis

Orchards historical

Data

Manage Pheromone trap plant

HistoricalData

analysis

Orchards historical

Data

Orchards Data

Producer

Manage Pheromone trap plant

HistoricalData

analysis

Orchards historical

Data

Orchards Data

Producer

Manage Pheromone trap plant

HistoricalData

analysis

Orchards historical

Data

Orchards Data

Producer

Manage Pheromone trap plant

HistoricalData

analysis

Orchards historical

Data

Orchards Data

Producer

Advisor

Manage Pheromone trap plant

HistoricalData

analysis

Query

Results

AOSE-2003, Melbourne July 15th 13

Model Assessment & Refinement (3)

• Is It possible for the Advisor to perform historical data analysis without consulting the Producer?

NONCRITICAL Producer FOR HistoricalDataAnalysis

Manage Pheromone trap plant

HistoricalData

analysis

MonitoringDevices

data

Manage Pheromone trap plant

HistoricalData

analysis

MonitoringDevices

data

Advisor

Manage Pheromone trap plant

HistoricalData

analysis

Query

ResultsManage

Pheromone trap plant

HistoricalData

analysis

MonitoringDevices

data

Orchards historical

Data

Orchards DataProducer

AOSE-2003, Melbourne July 15th 14

Model Validation

The informal Analyst looks for relevant validation cases to be proposed to the stakeholder in order to drive the validation process and to end up with an agreed model

AOSE-2003, Melbourne July 15th 15

Model Validation

• How does the Advisor usually operate? Is that he/she always satisfies the goal area collection after satisfying all its sub-goals, according to the following sequence: area analysis via GIS, plant plan and finally dispenser report and order?

FULFILL AreaAnalysisViaGIS THEN PlantPlan THEN DispenserReportAndOrder THEN AreaCollection

DispenserReportAndOrder PlantPlan

AOSE-2003, Melbourne July 15th 16

Conclusion

• Lightweight usage of Formal Methods

• Formal model is extracted automatically by an annotated informal model

• Formal model properties to be verified are obtained from queries in a user friendly language

• Witnesses and counter-examples are graphical

AOSE-2003, Melbourne July 15th 17

Conclusion (2)

Informal Model

Natural Language Query

High Level Lang. Query

Formal Tropos Query

Visual Results

Graphical Editor

VerificationEngineFormal Tropos Results

AOSE-2003, Melbourne July 15th 18

Future Work

Informal Model

High Level Lang. Query

Formal Tropos Query

Visual Results

Graphical Editor

VerificationEngine

(NuSMV)Formal Tropos Results

MODELER

TH

E T

OO

L Visual Query

AOSE-2003, Melbourne July 15th 19

Future Work

• We are validating the framework respect to other software development activities

• We are now involved in the design of the tool that supports:– The build up of the modeler components– The management of the informal diagram via graph

rewriting techniques– The high level language to temporal logic queries

translator– The implementation of visualization functions to show

the formal results to the informal analyst

AOSE-2003, Melbourne July 15th 20

References

• T-Tool: http://sra.itc.it/tools/t-tool• Tropos: http://science.unitn.it/tropos

AOSE-2003, Melbourne July 15th 21

LTL query formula

Global PossibilityF ( a:Advisor

( had:HistoricalDataAnalysis

(had.actor = a Fulfilled(had))))