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Social Structures in Tropos
Manuel Kolp
U Louvain
Paolo Giorgini John Mylopoulos
U Trento
U Toronto
First Tropos Workshop, Trento, 15-16 November 2001
Motivation

Narrowing the gap between requirements modeling and system
design

Same concepts for both phases: Social and intentional structures

Coordinated & autonomous with goals & social dependencies

Concepts from organization theory, … and early requirements
modeling

Ontology: 3 levels (Macro, micro, atomic)
Social Structures in Tropos 2
Social Ontology

3 Levels

1 Macrolevel : Organizational Styles (Organization Theory)
– Vertical Integration, Pyramid, Joint Venture, Structure in 5, Bidding,
Hierarchical Contracting, Co-optation, Takeover

2 Micro level : Social Patterns (Agent, COOPIS Community)
– Broker, Matchmaker, Contract-Net, Mediator, Monitor, Embassy,
Wrapper, Master-Slave, ...

3 Atomic : Social and intentional concepts – i*
– goals, actors, social dependencies, …
Social Structures in Tropos 3
Organization Theory

Mintzberg, Scott, Galbraith, …

Studies alternatives and models for (business) organizations

Model the coordination of business stakeholders -- individuals,
physical or social systems -- to achieve common (business) goals.
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Structure in 5

Operational core : basic operations -- the input, processing,
output associated with running the organization.

Strategic apex : executive, strategic decisions.

Support : Assists the operation core for non-operational services
outside the basic flow of operational procedures.

Technostructure : standardizes the behavior of other
components, help the system adapt to its environment.

Middle line : Actors who join the apex to the core.
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Structure in 5 and Joint Venture
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Bidding and Vertical Integration
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Structure in 5 in detail (from Mintzberg)
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Formal Analysis
Dependency StrategicManagement
Type SoftGoal
Mode achieve
Depender MiddleAgncy
Dependee Apex
Attribute constant objective : MiddleAgencyObjective
Creation
condition objective.strategy
trigger
Pursue(objective)
Fulfillment
condition for depender
 ma-strategy: MiddleAgencyStrategy
( org -strategy: OrgStrategy
(objective.strategy=strategy ^
consistent(ma-strategy,org-strategy))
[the StrategicManagement dependency is created when there is no strategy for a
given middle agency objective, and it is fulfilled when there exists a middle agency
strategy consistent with all the strategies of the organization]
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The Mobile Robot Case Study

Mobile robot activities:
- Acquiring the input from sensors,
- Controlling the motion of moveable parts,
- Planning its future path.

External Factors:
- Obstacles may block the path,
- Sensor inputs may be imperfect,
- The robot may run out of power,
- Mechanical limitations may restrict accuracy
- The robot may manipulate hazardous materials,
- Unpredictable events may leave little time for responding.
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Conventional Architectures
Control Loop
Task Trees : Hierarchies of tasks. Parent tasks
initiate child tasks. Temporal dependencies
between tasks permit selective concurrency.
Layers
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Organizational Architectures: Structure-in-5
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Quality Attributes for Mobile Robots

Coordinativity. A mobile robot has to coordinate the actions it
undertakes to achieve its objective with the reactions forced on it by the
environment.

Predictability. For a mobile robot, never will all the circumstances of
the operation be fully predictable. The architecture must provide the
framework in which the robot can act even when faced with incomplete
information.
Failability-Tolerance. Must prevent the failure of the robot’s operation
and its environment. Local problems like reduced power supply,
unexpectedly opening doors should not necessarily imply the failure of
the mission.
Adaptability. Application for mobile robots frequently requires
experimentation and reconfiguration. Changes in assignments require
regular modification.


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Strengths and Weaknesses of Robot Architectures
Loop
Layers
Task Tree
S-in-5
Joint-Vent.
Coordinativity
-
-
+-
++
++
Predictability
+-
+
+-
+
++
Failability-Tol.
+
+-
+
+
+
Adaptability
+-
+-
+
+
+-
Social Structures in Tropos 14
Coordinativity

Control loop: Simplicity is a drawback when dealing with complex tasks,
no leverage for decomposing the software into more precise components.

Layers: services and requests between adjacent layers. Transactions not
always straight-forward. Need to skip layers to coordinate behavior.

Task trees: clear separation of action and reaction. Allows incorporation of
concurrent agents. Components have little interaction with each other.

Structure-in-5: separates data (sensor control, interpreted results, world
model) from control (motor, navigation, scheduling, planning and userlevel) hierarchies

Joint venture: Components interact via the joint manager for strategic
decisions. They indicate their interest, the joint manager returns them
such information or mediates the request to other partner component.
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NFR Analysis: Selecting Architectures
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Mobile Robot Organizational Environment
With the Bidding Style
Bidder
0. task
auctionned
Issuer
Auctioneer
Bidder
Bidder
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Using These Social Structures at All Steps

Early requirements (organization modeling): stakeholders
(people, organizations, systems), goals and dependencies.

Late requirements, the system-to-be as one or a few social
actors (blackbox) participating in the organization model.

Architectural design, the system as an organization of actors

Detailed design, system actors transformed into agents by
means of social patterns

Implementation: Multi-agent system as societies of
individuals to achieve particular, possible common goals.
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Media Industry: Early Requirements
Organization Modeling
with the Joint Venture
Style
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Media Industry: Late Requirements
With the
Bidding Style
With the Vertical
Integration Style
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Media Industry: Architectural Design
E-business styles:
on web, protocols,
technologies
Not on business
processes, NFRs
No organization of
the architecture,
conceptual highlevel perspective
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Social Patterns
Mediator
Embassy
Contract-Net
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Detailed Design with Social Patterns
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Conclusion

System described with concepts from requirements and
organization modeling

 Narrows the gap requirements / design

Multi-Agent Architectures as social and intentional structures

Best suited to open, dynamic and distributed applications

Ontology on 3 levels:
– Macro: Organization Styles
– Micro: Social Patterns
– Atomic: i* - goals, actors, social dependencies, …
Social Structures in Tropos 24
Discussion: Problems, Suggestions ???

Organization Theory why not Sociology, Group Dynamics, …

Formalization at the metalevel: Makes sense, not too abstract??

Formal result: ex.: sound and complete, instantiation ethics

Convincing real-world size case study: Organization Modeling,
Early (Business) Requirements

Styles vs Patterns Macro level <-> Microlevel

Convincing for organization theorists, sociologists, ontologists??

NFR evaluation: intuitive vs formal for Requirements/Architectures

WRT Conventional Architectures: pros & cons, reevaluation

Methodology: Social Structures at all steps makes sense?
Social Structures in Tropos 25