07 software connectors

1. Copyright © Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy. All rights reserved.
Software Connectors
Software Architecture
Lecture 7

2. Software Architecture: Foundations, Theory, and Practice
What is a Software Connector?
Architectural element that models
uInteractions among components
uRules that govern those interactions
Simple interactions
uProcedure calls
uShared variable access
Complex & semantically rich interactions
uClient-server protocols
uDatabase access protocols
uAsynchronous event multicast
Each connector provides
uInteraction duct(s)
uTransfer of control and/or data 2

3. Software Architecture: Foundations, Theory, and Practice
Where are Connectors in Software
Systems?
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Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.

4. Software Architecture: Foundations, Theory, and Practice
Implemented vs. Conceptual
Connectors
Connectors in software system implementations
uFrequently no dedicated code
uFrequently no identity
uTypically do not correspond to compilation units
uDistributed implementation
Across multiple modules
Across interaction mechanisms
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5. Software Architecture: Foundations, Theory, and Practice
Implemented vs. Conceptual
Connectors (cont’d)
Connectors in software architectures
uFirst-class entities
uHave identity
uDescribe all system interaction
uEntitled to their own specifications & abstractions
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6. Software Architecture: Foundations, Theory, and Practice
Reasons for Treating Connectors
Independently
Connector ¹ Component
uComponents provide application-specific functionality
uConnectors provide application-independent
interaction mechanisms
Interaction abstraction and/or parameterization
Specification of complex interactions
uBinary vs. N-ary
uAsymmetric vs. Symmetric
uInteraction protocols
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7. Software Architecture: Foundations, Theory, and Practice
Treating Connectors Independently
(cont’d)
Localization of interaction definition
Extra-component system (interaction) information
Component independence
Component interaction flexibility
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8. Software Architecture: Foundations, Theory, and Practice
Benefits of First-Class Connectors
Separate computation from interaction
Minimize component interdependencies
Support software evolution
uAt component-, connector-, & system-level
Potential for supporting dynamism
Facilitate heterogeneity
Become points of distribution
Aid system analysis & testing
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9. Software Architecture: Foundations, Theory, and Practice
An Example of Explicit Connectors
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Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.

10. Software Architecture: Foundations, Theory, and Practice
An Example of Explicit Connectors
(cont’d)

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Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.

11. Software Architecture: Foundations, Theory, and Practice
Software Connector Roles
Locus of interaction among set of components
Protocol specification (sometimes implicit) that defines its
properties
uTypes of interfaces it is able to mediate
uAssurances about interaction properties
uRules about interaction ordering
uInteraction commitments (e.g., performance)
Roles
uCommunication
uCoordination
uConversion
uFacilitation
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12. Software Architecture: Foundations, Theory, and Practice
Connectors as Communicators
Main role associated with connectors
Supports
uDifferent communication mechanisms
e.g. procedure call, RPC, shared data access, message
passing
uConstraints on communication structure/direction
e.g. pipes
uConstraints on quality of service
e.g. persistence
Separates communication from computation
May influence non-functional system characteristics
ue.g. performance, scalability, security
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13. Software Architecture: Foundations, Theory, and Practice
Connectors as Coordinators
Determine computation control
Control delivery of data
Separates control from computation
Orthogonal to communication, conversion, and
facilitation
uElements of control are in communication, conversion
and facilitation
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14. Software Architecture: Foundations, Theory, and Practice
Connectors as Converters
Enable interaction of independently developed,
mismatched components
Mismatches based on interaction
uType
uNumber
uFrequency
uOrder
Examples of converters
uAdaptors
uWrappers
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15. Software Architecture: Foundations, Theory, and Practice
Connectors as Facilitators
Enable interaction of components intended to
interoperate
uMediate and streamline interaction
Govern access to shared information
Ensure proper performance profiles
ue.g., load balancing
Provide synchronization mechanisms
uCritical sections
uMonitors
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16. Software Architecture: Foundations, Theory, and Practice
Connector Types
Procedure call
Data access
Event
Stream
Linkage
Distributor
Arbitrator
Adaptor
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17. Software Architecture: Foundations, Theory, and Practice
A Framework for Classifying
Connectors
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Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.

18. Software Architecture: Foundations, Theory, and Practice
Procedure Call Connectors
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Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.

19. Software Architecture: Foundations, Theory, and Practice
Event Connectors
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Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.

20. Software Architecture: Foundations, Theory, and Practice
Data Access Connectors
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Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.

21. Software Architecture: Foundations, Theory, and Practice
Linkage Connectors
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Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.

22. Software Architecture: Foundations, Theory, and Practice
Stream Connectors
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Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.

23. Software Architecture: Foundations, Theory, and Practice
Arbitrator Connectors
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Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.

24. Software Architecture: Foundations, Theory, and Practice
Adaptor Connectors
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Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.

25. Software Architecture: Foundations, Theory, and Practice
Distributor Connectors
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Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.

26. Software Architecture: Foundations, Theory, and Practice
Discussion
Connectors allow modeling of arbitrarily complex
interactions
Connector flexibility aids system evolution
uComponent addition, removal, replacement,
reconnection, migration
Support for connector interchange is desired
uAids system evolution
uMay not affect system functionality
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27. Software Architecture: Foundations, Theory, and Practice
Discussion
Libraries of OTS connector implementations allow
developers to focus on application-specific issues
Difficulties
uRigid connectors
uConnector “dispersion” in implementations
Key issue
uPerformance vs. flexibility
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