software engineering - chp5- software architecture

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Chapter 5 – Software Architecture

How to define the architecture of your software product

Dr. L i l ia SFAXIwww. l i l iasfax i .wix .com /l i l iasfax i

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MedTech – Mediterranean Institute of TechnologyCS321-Software Engineering

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SOFTWARE ARCHITECTURE - DEFINITIONSoftware Architecture

Dr. L i l ia SFAXI www. l i l iasfax i .wix .com /l i l iasfax i

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Software Architecture

• Architecture• « Architecture is the fundamental organization of a system, embodied in its

components, their relationships to each other and the environment, and the principles governing its design and evolution. » [ANSI/IEEE Std 1471-2000]

• Software Architecture• « The software architecture of a program or computing system is the

structure or structures of the system, which comprise software elements, the externally visible properties of those elements, and the relationshipsamong them. »[SEI]


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Software Architecture - Definition

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Software Architecture

• Mainly: Architecture Defines Structure• Decomposition of system into :

• Software Elements• Elements are captured as abstractions

• Correspond to high level system modules or components

• Component interfaces• External visible properties of elements

• Describe element features exposed to others

• Typically represent services provided to other elements

• Component responsibilities• What does a component precisely do?

• Relationships of elements• How do elements interact with others?


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Software Architecture Structures Examples


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Modules Components and Connections

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Software Architecture Structures Examples


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Distribution

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Structures from Multiple Views


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• Large software systems require structures from multiple perspectives (views)• A single view is not sufficient to address all the requirements

• Examples of views• Context View

• Focuses on the system’s functionality

• Deployment View• Reflects the physical deployment of software components to computing

hardware

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Analogy : Building Architecture Views


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2D Front View

Floor Plan View

Room Plan View

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Why Using Software Architecture?

• Crucial changes in software engineering have increased the importance of architecture• Scale

• Distribution

• Security


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Minimally Distributed System

Highly Distributed System

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A Good Software Architecture…

• Considers for the system:• The functional requirements• The non functional requirements• The entire system lifecycle

• Helps us understand the system:• Divides the system meaningfully• Abstract complicated details

• Provides the framework for:• Realization• Project Planning • Project Organization

• Integrate all the development artefacts• Provide documentation


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Software Architect

The ideal Software Architect should be a man of letters, a mathematician, familiar with historical studies, a dilifent

student of philosophy, acquainted with music, not ignorant of medicine, learned in the responses of juriconsults, familiar with

astronomy and astronomical calculations.

Vitrivus (Roman author, architect and civil engineer, during the 1st century BC)


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Software Architect and Others


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SOFTWARE ARCHITECTURE PATTERNSSoftware Architecture


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Architectural Patterns

• An architectural pattern in a proven structural organization schema for software systems

• Architectural Patterns vs Design Patterns (already seen in chapter 4)• Design Patterns offer a common solution for a common problem in the form

of classes working together• Smaller in scale than architectural patterns, where the components are

subsystems rather than classes

• Design Patterns do not influence the fundamental structure of a system• Only affect a single subsystem

• They may help implementing an architectural pattern

• Some (not all) architectural patterns are described here-after


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Software Architecture Patterns

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Pattern 1: Layers Pattern

• Helps structure applications that can be decomposed into groups of subtasks, each of which is at a particular level of abstraction

• Each layer provides services to the next higher layer• Services in a layer are implemented using services from the next lower

layer• Service requests are frequently done by using synchronus procedure

calls

• Most famous example of layered systems: networking protocols


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Pattern 1: Layers Pattern (Example 1)


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Networking Protocol(OSI Model)

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Pattern 1: Layers Pattern (Example 2)


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Pattern 2: Client-Server Pattern

• A server component provides services to multiple client components• A client component requests services from the server component

• Servers are permanently active, listening for clients• Client and server may reside in different machines

• This pattern can be considered as a form of the layered pattern withtwo layers, the clients being the higher level and the server the lowerlevel

• Examples• Remote database access

• Remote file systems access• Web-based applications (browsers request from a web server)


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Pattern 2: Client-Server Pattern (Example)


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Pattern 3: Master-Slave Pattern

• Supports fault-tolerance and parallel computation

• The master component distributes the work among identical slave components, and computes a final result from the results they return

• Applied for instance in :• Process control

• Embedded systems

• Large scale parallel computations• Fault-tolerant systems


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Pattern 3: Master-Slave Pattern (Example)


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Pattern 4: Pipe-Filter Pattern

• Provides a structure for systems that produce a stream of data• Each processing step is encapsulated in a filter component

• Data is passed through pipes• Pipes can be used for buffering or for synchronization

• This pattern divides the task of a system into several processing steps

• The steps are connected by the data flow• The output of a step is the input for the next step

• Common examples: • Pipe-filter in the unix shell commands

• cat fi le | grep xyz | sort | uniq > out

• Compilers


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Pattern 4: Pipe-Filter Pattern (Example)


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Compiler

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Pattern 5: MVC Pattern

• Model-View-Controller Pattern• An interactive application is divided into three parts:

• Model• Contains core fundtionality and data

• View• Displays the information to the user

• Controller• Handles the input from the user

• Often uses the Observer design pattern• User input can invoke a change in the model, and in the displayed view

• Makes it easy to have multiple views of the same model


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