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Lecture 15

Enterprise

Systems

Development( CSC447)

COMSATS Islamabad

Muhammad Usman, Assistant Professor

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Component and Connector ViewType

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Overview

• Defines models consisting of

– elements having some runtime presence – processes, objects, clients, servers, data stores

– Pathways of interaction – communication links, protocols, information flows, access to shares storage

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Runtime entities and their interactions

• May contain many instances of the same component type

• Similar to object(collaboration) diagrams as against class diagrams(which define types of elements)

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Summary of C&C ViewtypeElements Component Types: principal processing

unit and datastores

Connector Types: interaction mechanisms

Relations Attachments:component ports are associated with specific connector roles

Properties of elements

Component: Name, type(general functionality, number and type of ports)

Other properties(like performance..)

Connector: name, type(nature of interaction, number and type of roles..), other properties(protocol of interaction, performance values..)

Topology No Inherent constraints

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C&C Viewtype Styles

• Pipe-and-filter

• Shared-data

• Publish-subscribe

• Client-server

• Peer-to-peer

• Communicating processes

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Components

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Component Interfaces

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Connectors

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Connector Roles

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Connector Role Examples

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Relations

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What is C&C for?

• To reason about runtime system quality attributes – performance, reliability, availability

• What are the systems principal executing components and how do they interact

• What are the major shared data resources

• Which parts of the system are replicated and how many times

• How does data progress through a system as it executes

• What protocols of interaction are used by communicating entities

• What parts of the system run in parallel

• How can the system’s structure change as it executes

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What is C&C not for?

• Can not represent design elements which do not have a runtime presence

• Example – interface of an element - usability

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C&C Viewtype Styles

• Pipe-and-filter

• Shared-data

• Publish-subscribe

• Client-server

• Peer-to-peer

• Communicating processes

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From Clements etal

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Pipes and Filters

• A filter transforms data that it receives from one or more pipes and transmits through one or more pipes

• A pipe is a connector that conveys streams of data from output port of one filter to input port of another

• Pipes buffer data

• The overall function is a composition of filter functions

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What for ..

• Very useful in data transformation

– Signal processing

– compilers

• To reason about system performance, stream latency, pipe buffer requirements, schedulability

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Pipes and filters - summary

Elements Component Types: filter – ports must be input or output

Connector Types: pipes – have data-in and data-out roles

Relations Attachments: associates filter output ports to data-in roles of a pipe and.. Out to in

Properties of elements Component: Name, type(general functionality, number and type of ports)

Other properties(like performance..)

Connector: name, type(nature of interaction, number and type of roles..), other properties(protocol of interaction, performance values..)

Topology Might be restricted to acyclic graphs

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Relationship with other styles

• Different from data flow projections/views

• In pipes-and-filters lines have specific meaning – transmit streams of data

• In dataflow relationships implies data communication – could be implemented as a procedure call, publish-subscribe, via a pipe..

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Shared data style

• Useful in exchange of persistent data, which has multiple accessors

• How does the consumer know data is available?

– Store informs the consumer – blackboard

– Consumer is responsible - repository

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Shared data access -summary

Elements Component types: data stores, data accessors

Connectors: data reading and writing

Relations Which accessor is connected to which store

Computational model Communication between accessors mediated by the store; communication may be initiated by either

Properties Same as in C&C; types of data, data performance, data distribution

Topology Data accessors are attached to connectors that are attached to stores

Elements Component types: data stores, data accessors

Connectors: data reading and writing

Relations Which accessor is connected to which store

Computational model Communication between accessors mediated by the store; communication may be initiated by either

Properties of elements Same as in C&C; types of data, data performance, data distribution

Topology Data accessors are attached to connectors that are attached to stores

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What for..

• Used when there are multiple accessors and persistence

• Decouple producer from consumer

• Data store performance, security, privacy, compatibility with other stores…

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Similarity to others

• Client-server style

• Publish-subscribe is similar without persistence

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Publish-subscribe styles

• Components interact via announced events

• Components subscribe to a set of events

• P-S runtime ensures that each published event is delivered to all subscribers

• The connector is an event bus

• Used in message production/consumption

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P-S summary

Elements Component types: any component with a pub/sub interface

Connectors: publish-subscribe

Relations Attachment associates components with pub-sub connector

Computational model A system of independent components that announce events and react to other announced events

Properties of elements Same as in C&C;

Topology All components are connected to an event distributor

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Where to use ..

• To send events and messages to recipients

• Set of recipients are unknown – can be added dynamically

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Client-Server

• Components interact by requesting services of other components

• Communication is initiated by a client

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Client-Server summary

Elements Component types: clients – which ask for services; servers –which provide services

Connectors: request-reply

Relations Attach clients to servers

Computational model Clients initiate activity and wait for results

Properties Same as in C&C; number and type of clients, performance

Topology Unrestricted; number of clients; tiers

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What for..

• Assignment of functionality is clear

• Can be independently assigned to tiers

• Can be used to argue about performance

• Example - WWW

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Peer-to-peer

• Components interact with each other exchanging services

• No asymmetry as in client-server

• Connectors are bidirectional

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Allocation Viewtype

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Allocation viewtype styles

• Deployment style

• Implementation style

• Work assignment style

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Summary of Allocation ViewtypeElements Software elements and environment

elements

Relations Allocated-to. A software element is allocated to an environmental element

Properties of elements

A software element has required properties. An environmental element has provided properties that need to be matched.

Topology Varies by style

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Deployment style

• Elements of the C&C styles are allocated to execution platforms

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Deployment style summary

Elements Software element: usually a process from the C$C view

Environmental Element: computing hardware, processor, disk, ..

Relations Allocated to: showing the physical unit the element resides

Migrates-to, copy-migrates to: if the allocation is dynamic

Properties of elements Required properties of software elements

Provided properties of software elements

Properties of relations Allocated to – either static or dynamic

Topology unrestricted

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From Clements etal

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Common Architectural Styles (Adapted from Shaw and Garlan)

• Dataflow systems

– Batch sequential

– Process control

– Pipes and filters

• Call-and-return systems

– Main program and subroutine

– Object-oriented systems

– Hierarchical layers

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Common Architectural Styles (Cont’d)• Independent components

– Communicating processes

– Event systems

• Virtual machines

– Interpreters

– Rule-based systems

• Repositories

– Databases

– Hypertext systems

– Blackboards

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Reference

• Bass, L., Clements, P. and Kazman, R., Software Architecture in Practice, Second Edition (2006), Addison-Wesley.

• Clements, P., Bachmann, F., Bass, L., Garlan, D., Ivers, j., Little, R., Nord, R. and Stafford, J., Documenting Software Architectures: Views and Beyond, 2002, Addison-Wesley. Documenting Software Architectures