Software Connectors
Software Architecture
Importance of Connectors
• Complex, distributed, multilingual, modern
software system functionality and managing data
is definitely undoubtedly very difficult
• At the same time achieving integration and
proper interaction between these components is
also equally important and more challenging than
just creating components
• In modern systems this important job of
interaction and connection is achieved by
connectors
Components and Connectors
• Connector  Component
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Components encapsulate functionality and data
Components provide application-specific functionality
Connectors encapsulate interaction
Connectors provide application-independent
interaction mechanisms
– Connectors perform transfer of control and data
among components. Basically they provide facilities to
components
– Persistence, invocation, messaging & transaction
– Complex components results in making interaction
critical
What is a Software Connector?
• Architectural element that models
– Interactions among components
– Rules that govern those interactions
• Simple interactions
– Procedure calls
– Shared variable access
• Complex & semantically rich interactions
– Client-server protocols
– Database access protocols
– Asynchronous event multicast
• Each connector provides
– Interaction duct(s)
– Transfer of control and/or data
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• Being application independent, connectors help us to
understand how the system works without knowing what
system does
• Connectors support abstraction and separation of concerns
• Many system properties can be derived from system
connectors
• Example of how connectors specify characteristics of the
system
– ‘Unix pipe connecting two components’ is the description of system
which provide high- level view of the system
– High level view specify model of the system and properties of
communication but not all properties of pipe
– It provides uniform stream of data, it consist of single interaction
channel and facilitate only unidirectional data transfer
Role of Connectors
• Connectors facilitate components by providing
different services:
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Communication
Coordination
Conversion and
Facilitation
• Based on these services connectors have four different
roles
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Communicator
Coordinator
Convertor and
Facilitator
Connectors as Communicators
• Main role associated with connectors
• Supports
– Different communication mechanisms
• e.g. procedure call, RPC, shared data access, message passing
– Constraints on communication structure/direction
• e.g. pipes
– Constraints on quality of service
• e.g. persistence
• Separates communication from computation
• May influence non-functional system characteristics
– e.g. performance, scalability, security
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Connectors as Coordinators
• Determine computation control
• Control delivery of data
• Function call and method invocation are
simple examples
• Signal and load balancing connectors
• Separates control from computation
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Connectors as Converters
• Enable interaction of independently developed,
mismatched components
• Mismatches based on interaction
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Type
Number
Frequency
Order
• Examples of converters
– Adaptors
– Wrappers
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Connectors as Facilitators
• Services like load balancing, concurrency control,
scheduling services are part of communication
• Enable interaction of components intended to
interoperate
– Mediate and streamline interaction
• Govern access to shared information
• Provide synchronization mechanisms
– Critical sections
– Monitors
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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.
A Framework for Classifying
Connectors
• Framework for studying connectors is divided into
different layers
• Top layer is Category which represents the broad
interaction role the connectors fulfill
• 2nd layer is Type; which differentiate connectors based
on the way in which the connector’s interact services
are realized
• 3rd layer is dimensions and sub dimensions.
Dimensions are architecturally relevant details of each
connector type
• 4th & lowest layer in the connector framework is
formed by the set of values a dimension can take
Connector Types
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Procedure call
Data access
Event
Stream
Linkage
Distributor
Arbitrator
Adaptor
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Procedure Call Connectors
• Transfers the control between two procedure/
subroutines by providing coordination service
• Transfer data like return value and works as a
communicator
• Most widely used and best understood
connectors
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.
• Synchronous: instant reply is expected e.g.
chatting
• Asynchronous: time is provided for
communication e.g. email
• Cardinality: fan in and fan out
– Connections available with the system
• Accessibility: private, protected or public
Event Connectors
• Events are system or language level messages
• Event is an instantaneous effect of the termination of
an invocation of an operation on an object which
occurs at that object’s location
• Provides coordination and communication services
• Creates virtual connection between components
interested in same events
• Dynamically this connection can appear or disappear
based on component’s interest
• Distributed applications with asynchronous
communication used these connectors
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.
Data Access Connectors
• Transfer of data between heterogeneous
components
• Provides communication serves by
transferring data
• Provides conversion service
• Data store can be temporary or persistent
• Persistent Data denotes information that is
infrequently accessed and not likely to be
modified
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.
Linkage Connectors
• Tie the system components together
• Establishes channel for communication or
coordination
• Once the channel is established, linkage
connectors can disappear or remain in the
system
• Provides facilitation
• Not a rich connector in terms of dimensions
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.
Stream Connectors
• Majorly use for communication purpose only
• Transferring large amount of data between
autonomous processes
• Streams are used in client server system with
data transfer protocol to deliver result of
computation
• Can be Combined with data access connector for
managing database of file storage
• Can be combined with event connector to
multiplex the delivery of large number of events
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.
Arbitrator Connectors
• When components are aware of presence of other
components but can not make assumption about their
needs and state, arbitrator streamline system operates
and resolves any conflicts (facilitation) and redirect the
flow of data (coordination)
• Multithreaded system for using shared memory uses
synchronization and concurrency control to guarantee
atomicity and consistency
• Arbitrator also acts as a mediator to provide services
like reliability and atomicity
• Security, safety, trustworthiness is also provided by
arbitrator connector
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.
Adaptor Connectors
• Provides facility to support interaction
between components that have not been
designed to interoperate
• It acts as convertor
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.
Distributor Connectors
• Performs identification of interaction paths
and subsequent routing of communication
and coordination
• These connectors does not act independently
but provides support to other connectors
• Distributed system exchanges information
using distributed connectors
• DNS routing, swiching
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.