Specialization in i* Strategic Rationale Diagrams

Lidia López, Xavier Franch, Jordi Marco

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Outline

• Motivation and research question

• Antecedents

• Proposal

Notion of correctness

Specialization operations

• Conclusions and related work

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MotivationTwo types of i* diagrams

SD diagrams

SR diagrams

They need to be synchronized

Customer

Name a Price

Buy Travel

Travel Agency

Travels Bought Easily

Easily Bought

CustomerTravel

AgencyEasily Bought

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Motivation

The is-a association represents a generali-zation, with an actor being a specialized case of another actor (ref. The i* Guide)

Our focus: specialization in i* through is-a

CustomerTravel

AgencyEasily Bought

Family

is-a

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Motivation

The ultimate effect of is-a is not clear:• The i* guide does not define it• i* modelers use it intuitively (and sometimes

inconsistently)

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Motivation

• How are the IEs belonging to Customer inherited in Family?

• What manipulations are valid over them? E.g., may Buy Travel have additional subtasks?

• Do Customer dependencies apply to Family?

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Research Question

Given an actor specialization relationship declared at the SD level, what modeling operations can be defined at the SR level?• What is the relevant background to make

this decision?• What are the effects of these operations?• What are the correctness conditions to be

fulfilled for their application?

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Strategy

Formulate an answer that aligns with:• the general concept of specialization in

the conceptual modeling community• the reported uses made by i* researchers • the preferences gathered empirically from

the community

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Analysis using Meyer’s Taxomania rule: “Every heir must introduce a feature, redeclare an inherited feature, or add an invariant clause”.

Antecedents: conceptual modeling

Area Approach New feature Add Invariant Redeclare feature

Knowledge Representation

Strict NewAttributes

No No

Defeasible No Attribute Cancellation

OO Languages

Simula 67

New Properties &

Methods

Simulation accessing properties via methods

No

Smalltalk-80, Delphi, C++, C#, Java

Overrides for methodsSimulation for properties

accessing via methods

Visual Basic Overrides and Shadows for properties and methods

Eiffel Adding invariantsRenaming and Redefinition for routines and procedures using

contracts

Conceptual Modeling

Semantic data modelsNew

Attributes & Methods

No No

UML No No

Borgida & Mylopoulos Attributes No

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Reported uses

Regularly used but RQ not answered

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Community perception: a survey

21 valid responses (July-Sept. 2010; 4th i* wks.)• 57% use sometimes, often or very often is-a links in their i* models

• 84% have doubts about its usage• 85%-90% allow for addition of elements

(dependencies / IEs)• 14%-38% allow for modification of elements• 5%-10% do not allow for removals of

elements

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As a result…From the three different possibilities:• Extension: a new IE or dependency,

related somehow to inherited elements, is added to the subactor.

• Redefinition: an IE or dependency that exists in the superactor is changed in the subactor.

• Refinement: the semantics of an inherited IE or dependency is made more specific.

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• Algebraic formalization: see paper Some simplifications made

• Actor specialization correctness: sat(a, M) sat(b, M)

• Actor correctness: sat(ie, M) = iemainIEs(a): sat(ie, M)

b

a

is-a

Notion of correctness

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Notion of correctness• IE correctness:

ie not decomposed: given by user ie decomposed: see decomposition

task-decomposition: sat(ie, M) sat(iesub, M)means-end: sat(iemeans, M) sat(ie, M)

ie with contributions (softgoal): Horkoff&Yu’s rules ie with outgoing dependencies: sat(ie, M) sat(iedep, M)

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Definition of operations• The paper introduces 5 different operations (2

for extension, 3 for refinement)• For each operation:

Definition: signature precondition postcondition (effects)

Theorem: actor specialization correctness is kept always by induction

• I’m not going to do that here!!

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Extension operations• OP1: IE extension with decomposition link:

Remark: please notice the graphical convention

TA

FTA

is-aTravels

Contracted Increased

Assistence Provided

Customers Attracted

Family Facilities Offered

Provide Child

Discounts

Provide Familiar

Destinations

Many Kind of Travels Offered

Good Quality-Price

RateHelp

Help

Travels Contracted Increased

Attractive Products

Good Quality-Price

Rate

Many Kind of Travels Offered

OR OR

Help

UTA

Search Trip by

Destination

Search Trip by

Conference

Get Travels

Name a Price

is-a

Name a Price

Sell Travels

Book Travel

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Extension operations• OP2: Addition of new main IEs

Services Provider

Many Transactions Processed

Profit Increased

Customer data sold to 3rd

Hurt

Travel Services Provider Travel Services

Provided

Encrypt Data

Contract Travels

List Offerings

is-a

Costs Reduced

Encrypt Data

Hurt

Privacy Kept

Help

Help

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Refinement operations• OP3: IE refinement

the implication given by correctness definition needs to be preserved

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Refinement operations• OP4: contribution link refinement

always keeping the “polarity” of the value

Assistance Provided

Asynchronous Support

Synchronous Support

TA

is-a

Assistance Provided

Provide Hotline

Travels Contracted

Easily

Help

Travels Contracted

Easily

Make

Synchronous Support

FTA

Travels Bought Easily

Assistance Obtained

Help

Customer

Family

is-a

Travels Bought Easily

Make

[Telephone]Assistance Obtained

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Refinement operations• OP5: dependency refinement

either dependum (IE) or strength (not in the paper!!)

Customer Info

Unversity&[Customer Info]

is-a

Researcher

Customer TA

UTA

is-a

Book Travel

Book Travel

Contract Travel

Contract Travel

XConference [Travel Offerings]

Name a PriceConference

[Travel Offerings]

Travel OfferingsName a Price

Travel Offerings

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ConclusionsResearch questions answered:

What modeling operations can be defined at the SR level?• What is the relevant background to make

this decision?• What are the effects?• What are the correctness conditions to be

fulfilled for their application?

What modeling operations can be defined at the SR level? EXTENSION & REFINEMENT• What is the relevant background to make

this decision? SOTA & SURVEY• What are the effects? FORMAL DEFINITION• What are the correctness conditions to be

fulfilled for their application? SATISFACTION NOTION

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Future work• Consider also redefinition• Ontological meaning for specialization• Apply same strategy for other types of actor

links

Hope youliked it!

Contact: Lidia López<llopez@lsi.upc.edu>