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Overview of iStar 2.0 Language Guide
This presentation is based on:
Dalpiaz, F., Franch, X. and Horkoff, J. (2016) iStar 2.0 language guide. arXiv preprint arXiv:1605.07767.
Eric, S. Y. (1995). Modelling strategic relationships for process reengineering. PhD Thesis. Department of Computer Science, University of Toronto.
Camilo C. Almendra
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Summary
Context and Motivation Language guide for version 2.0 Comparison with original version Conclusions
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iStar 2.0
Context iStar “1.0” released in 1995 (Eric Yu’s PhD Thesis) Highly active research community on GORE and iStar Too much diversity of extensions and variations (Horkoff
et al. 2014) Problems
Difficulty to learn and teach Lack of core reference for professional usage Fragmentation of tool development
Horkoff, J., Li, T., Li, F. L., Salnitri, M., Cardoso, E., Giorgini, P., ... & Pimentel, J. (2014). Taking goal models downstream: a systematic roadmap. In Research Challenges in Information Science (RCIS), IEEE Eighth International Conference on.
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iStar 2.0 Initiative
Purpose Establish core fundamental concepts and rules Keep language open to tailoring Foster framework usage outside research community
Timeline Oct’14: initial community meeting Jun’15: standardization committee was formed Aug’15, Oct’15: initial draft discussions Dec’15: preliminary version discussions Mar’16: final version released Jun’16: minor improvements
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iStar 2.0 Language Guide
Standardization process Based on Eric Yu’s thesis and seminal paper Discussions with experts to identify core improvements Focus on concepts and relationships
Out of scope Ontological definition of constructs Visual notation improvements Methodological issues
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iStar 2.0 Language Guide
Structure Actor and actor types Actor association links Intentional elements Social dependencies Intentional element links Model views Metamodel
Differences from original version will be highlighted
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Actors and Actor Types
Actors Active, autonomous entities that aim at
achieving their goals by exercising their know-how, in collaboration with other actors
Generic Used when type is not relevant (yet)
Role Abstract characterization of the behavior of a
social actor Agent
Actor with concrete, physical manifestations
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Actors and Actor Types
Position actor (original version) Intermediary abstraction
between a role and an agent Set of roles typically played by
one agent Agent occupies a Position Position covers a Role
Removed from 2.0 Position can be expressed using
actor association links (see next)
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Actors and Actor Types
Actor Boundary Container for actor’s intentional elements
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Actor Association Links
Association Links Binary links from a actor (source) to another single
actor (target) is-a
Represents specialization/generalization Only Roles can specialize other Roles Only Generic actors can specialize other Generic
actors Agents can not be specialized (they are concrete)
participates-in Any other kind of association When source and target are same type, it means
“part-of” When target is a Role, it means actor “plays” the
role.
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Actor Association LinksRepresenting “Position” actor from original version using iStar 2.0
participates-inparticipates-in
participate
s-in
Physician
occupies
playscovers
part of
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Intentional Elements
Goal State of affairs that the actor wants to achieve
Quality (softgoal in original) Attribute for which an actor desires some level of achievement
Task Represents actions that an actor wants to be executed
Resource Physical or informational entity that the actor requires in order to
perform a task
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Social Dependencies
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Dependency Arguments
depender Actor that depends for something (the dependum) to be provided
dependerElmt Intentional element within the depender’s actor boundary where the
dependency starts from, which explains why the dependency exists It can be ommited
dependum Intentional element that is the object of the dependency
dependee Actor that should provide the dependum
dependeeElmt Intentional element that explains how the dependee intends to provide the
dependum It can be ommited
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Social Dependencies
dependeeElmt ommitted or not yet defined
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Dependencies Semantics
Types of dependum Goal
Dependee is expected to achieve the goal, and is free to choose how Quality
Dependee is expected to sufficiently satisfy the quality, and is free to choose how
Task Dependee is expected to execute the task in a prescribed way
Resource Dependee is expected to make the resource available to the depender
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Intentional Element Links
Purpose Intentional elements from an actor’s intentionality can be related in four
different ways Each type of links represents a kind of influence
Refinement Used for Goals and Tasks, it provided a way to link them hierarchicaly
Needed-by Only used from Resources to Tasks, to indicate an actor needs a resource to
execute the task Contribution
It provided ways to represent effects of intentional elements on Qualities Qualification
It links Qualities to intentional elements to express desired attributes to be applied during goal achievements, task execution or resource provision
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Intentional Element Links
iStar 2.0 intentional elements possible relationships
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Intentional Element Links
Original versus 2.0
Refinement
Needed-by
Contribution
Contribution
Refinement
Refinement
Qualification
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Intentional Element Links
Refinements
AND-refinement: all sub-goals achieved/ sub-tasks performed
OR-refinement: At least one sub-goal achieved or sub-task performed
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Intentional Element Links
Needed-by
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Intentional Element Links
Contributions
Weakly Satisfies
Sufficiently Satisfies
Sufficiently Denies
Weakly Denies
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Intentional Element Links
Contributions (Softgoal-Task Link in original version)
Eric Yu’s original version examplifies positive and negative contributions using ‘+’ and ‘-’ signals.
It’s out of scope of his thesis to indicate a definitive framework/notation.
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Intentional Element Links
Qualification● It provides a more powerful representation of influences of
quality criteria in dependencies and intentional elements
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Model Views
Strategic Dependency (SD)
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Model Views
Strategic Rationale (SR)
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Model Views
Hybrid SD/SR (new!)
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Metamodel and Rules
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Metamodel and Rules Integrity constraints (some of them)
The is-a relationship applies only between pairs of roles or pairs of actors
There should be no is-a cycles There should be no participates-in cycles A pair of actors can be linked by at most one actor link: it is not
possible to connect two actors via both is-a and participates-in; In a dependency D, if the dependerElmt x exists, then the actor that
wants x is the same actor that is D’s depender ...
More rules are stated in the guide Rules promotes a more uniform usage of language
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Conclusions
iStar 2.0 Language Guide provides a more structured and uniform description of language constructs and rules Ease of learning and teaching Common baseline for extensions proposals
Relationships’ symbols overload is reduced Task Decomposition Links are divided into Refinements, Needed-
by and Qualification Means -ends Links are divided into Refinements and Contribution
Rules of association are established This eases dissemination of good practices and producing
compatible models between different practitioners Language still lacks a extension mechanism
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