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Copyright © Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy. All rights reserved. Software Connectors
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Foundations, Theory, and Practice Software Architecture 2 What is a Software Connector? Architectural element that models u Interactions among components u Rules that govern those interactions Simple interactions u Procedure calls u Shared variable access Complex & semantically rich interactions u Client-server protocols u Database access protocols u Asynchronous event multicast Each connector provides u Interaction duct(s) u Transfer of control and/or data
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Foundations, Theory, and Practice Software Architecture 3 Where are Connectors in Software Systems? Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.
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Foundations, Theory, and Practice Software Architecture 4 Implemented vs. Conceptual Connectors Connectors in software system implementations u Frequently no dedicated code u Frequently no identity u Typically do not correspond to compilation units u Distributed implementation Connectors in software architectures u First-class entities u Have identity u Describe all system interaction u Entitled to their own specifications & abstractions
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Foundations, Theory, and Practice Software Architecture 5 Benefits of First-Class Connectors Separate computation from interaction Minimize component interdependencies Support software evolution u At component-, connector-, & system-level Potential for supporting dynamism Facilitate heterogeneity Become points of distribution Aid system analysis & testing
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Foundations, Theory, and Practice Software Architecture 6 An Example of Explicit Connectors Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.
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Foundations, Theory, and Practice Software Architecture 7 An Example of Explicit Connectors (cont’d) ? Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.
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Foundations, Theory, and Practice Software Architecture 8 Software Connector Roles Locus of interaction among set of components Protocol specification (sometimes implicit) that defines its properties u Types of interfaces it is able to mediate u Assurances about interaction properties u Rules about interaction ordering u Interaction commitments (e.g., performance) Roles u Communication u Coordination u Conversion u Facilitation
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Foundations, Theory, and Practice Software Architecture 9 Connectors as Communicators Main role associated with connectors Supports u Different communication mechanisms e.g. procedure call, RPC, shared data access, message passing u Constraints on communication structure/direction e.g. pipes u Constraints on quality of service e.g. persistence Separates communication from computation May influence non-functional system characteristics u e.g. performance, scalability, security
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Foundations, Theory, and Practice Software Architecture 10 Connectors as Coordinators Determine computation control Control delivery of data Separates control from computation Orthogonal to communication, conversion, and facilitation u Elements of control are in communication, conversion and facilitation
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Foundations, Theory, and Practice Software Architecture 11 Connectors as Converters Enable interaction of independently developed, mismatched components Mismatches based on interaction u Type u Number u Frequency u Order Examples of converters u Adaptors u Wrappers
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Foundations, Theory, and Practice Software Architecture 12 Connectors as Facilitators Enable interaction of components intended to interoperate u Mediate and streamline interaction Govern access to shared information Ensure proper performance profiles u e.g., load balancing Provide synchronization mechanisms u Critical sections u Monitors
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Foundations, Theory, and Practice Software Architecture 13 Connector Types Procedure call Data access Event Stream Linkage Distributor Arbitrator Adaptor
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Foundations, Theory, and Practice Software Architecture 14 A Framework for Classifying Connectors Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.
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Foundations, Theory, and Practice Software Architecture 15 Procedure Call Connectors Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.
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Foundations, Theory, and Practice Software Architecture 16 Event Connectors Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.
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Foundations, Theory, and Practice Software Architecture 17 Data Access Connectors Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.
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Foundations, Theory, and Practice Software Architecture 18 Linkage Connectors Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.
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Foundations, Theory, and Practice Software Architecture 19 Stream Connectors Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.
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Foundations, Theory, and Practice Software Architecture 20 Arbitrator Connectors Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.
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Foundations, Theory, and Practice Software Architecture 21 Adaptor Connectors Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.
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Foundations, Theory, and Practice Software Architecture 22 Distributor Connectors Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.
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Foundations, Theory, and Practice Software Architecture 23 Discussion Connectors allow modeling of arbitrarily complex interactions Connector flexibility aids system evolution u Component addition, removal, replacement, reconnection, migration Support for connector interchange is desired u Aids system evolution u May not affect system functionality
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Foundations, Theory, and Practice Software Architecture 24 Discussion Libraries of OTS connector implementations allow developers to focus on application-specific issues Difficulties u Rigid connectors u Connector “dispersion” in implementations Key issue u Performance vs. flexibility
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Foundations, Theory, and Practice Software Architecture 25 How Do You Select a Connector? Determine a system’s interconnection and interaction needs u Software interconnection models can help Determine roles to be fulfilled by the system’s connectors u Communication, coordination, conversion, facilitation For each connector u Determine its appropriate type(s) u Determine its dimensions of interest u Select appropriate values for each dimension For multi-type, i.e., composite connectors u Determine the atomic connector compatibilities
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Foundations, Theory, and Practice Software Architecture 26 Simple Example System components will execute in two processes on the same host u Mostly intra-process u Occasionally inter-process The interaction among the components is synchronous The components are primarily computation-intensive u There are some data storage needs, but those are secondary
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Foundations, Theory, and Practice Software Architecture 27 Simple Example (cont’d) Select procedure call connectors for intra-process interaction Combine procedure call connectors with distributor connectors for inter-process interaction RPC Select the values for the different connector dimensions What are the appropriate values? What values are imposed by your favorite programming language(s)?
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Foundations, Theory, and Practice Software Architecture 28 Procedure Call Connectors Revisited Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.
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Foundations, Theory, and Practice Software Architecture 29 Distributor Connectors Revisited Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.
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Foundations, Theory, and Practice Software Architecture 30 Two Connector Types in Tandem Select the appropriate values for PC and RPC! Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John Wiley & Sons, Inc. Reprinted with permission.
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Foundations, Theory, and Practice Software Architecture 31 Composing Basic Connectors In many systems a connector of multiple types may be required to service (a subset of) the components All connectors cannot be composed u Some are naturally interoperable u Some are incompatible u All are likely to require trade-offs The composition can be considered at the level of connector type dimensions and subdimensions
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Foundations, Theory, and Practice Software Architecture 32 Well Known Composite Connectors Grid connectors (e.g., Globus) u Procedure call u Data access u Stream u Distributor Peer-to-peer connectors (e.g., Bittorrent) u Arbitrator u Data access u Stream u Distributor Client-server connectors Event-based connectors
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