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CS 425/625 Software Engineering

Architectural Design

Based on Chapter 11 of the textbook [SE-8] Ian Sommerville,Software Engineering, 8th Ed., Addison-Wesley, 2006 and on theCh11 PowerPoint presentation available at the book’s web-site:

www.comp.lancs.ac.uk/computing/resources/IanS/SE6/Slides/index.html

October 15, 2008

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Outline

Introduction System Organization Modular Decomposition Control Styles Reference Architectures

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Introduction….

Architectural (high-level) design = the process of establishing the subsystems of a larger software system and defining a framework for subsystem control and data communication

Software architecture = the output of the high-level design process

Defining and documenting the software architecture provides support for: Stakeholder communication System analysis Large-scale software reuse

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.Introduction…

The overall system architecture influences the system’s: Performance Security Safety Availability Maintainability

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..Introduction..

Distinction between subsystem and module: Subsystem = larger part of the system with quasi-

independent operation; depends little on other subsystems’ services, contains other subsystems and modules as well as interfaces for communicating with other subsystems

Module = non-independent system component that provides services to other modules; usually makes use of other modules’ services and contains simpler components

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…Introduction.

Common high-level design activities: System structuring (system organization):

identification of sub-systems and their communication paths

Modular decomposition: identification of modules and module interconnection within each subsystem

Control modeling: determination of control connections between subsystems (modules)

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….Introduction

Types of architectural design models: Static structural models Dynamic process models Interface models Relationship models Distribution models

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System Organization…..

System organization (system structuring) is focused on identifying subsystems and their communication links

Communications between subsystems involve both data and control

Block diagrams can be used for describing the system’s structure

The system’s architecture can be shown using more specific structural models, e.g.: Repository model Client-server model Layered model

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.System Organization….

The repository model shows a system’s architecture centered around a shared database

The client-server model is a distributed, network model that describes how operations and data are distributed across several processing units. Some of these units are servers, other are clients

The layered model (the abstract machine model) depicts the system as a series of layers, each layer representing an abstract machine and having assigned a subsystem

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..System Organization…

Example of a structural model depicted using a block diagram: a packing robot system [Fig. 11.1, SE-8]

Visionsystem

Objectidentification

system

Armcontroller

Grippercontroller

Packagingselectionsystem

Packingsystem

Conveyorcontroller

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…System Organization..

Example of repository model for system architecture: a CASE toolset [Fig. 11.2, SE-8]

Projectrepository

Designtranslator

Programeditor

Designeditor

Codegenerator

Designanalyser

Reportgenerator

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….System Organization.

Example of client-sever architecture: a movie and picture library [Fig. 11.3, SE-8]

Catalogueserver

Librarycatalogue

Videoserver

Film clipfiles

Pictureserver

Digitisedphotographs

Web server

Film andphoto info.

Client 1 Client 2 Client 3 Client 4

Internet

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…..System Organization

An abstract machine model: a version management system [Fig. 11.4, SE-8]

Configuration management system layer

Database system layer

Operating system layer

Object management system layer

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Modular Decomposition..

Modular decomposition means dividing each subsystem in modules and identifying interconnections between modules

Models described previously can be applied here as well (a subsystem is, in fact, a system, and the distinction between a subsystem and a module is relative)

Styles that may be used for decomposition: Object-oriented decomposition: a subsystem consists of

several communicating objects Function-oriented pipelining: functional modules are

identified, together with data transfer paths

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.Modular Decomposition.

Partial object model of an invoicing system [Fig. 11.5, SE-8]

issue ()sendReminder ()acceptPayment ()sendReceipt ()

invoice#dateamountcustomer

Invoice

invoice#dateamountcustomer#

Receipt

invoice#dateamountcustomer#

Payment

customer#nameaddresscredit period

Customer

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..Modular Decomposition

DFD of an invoicing system [Fig. 11.6, SE-8]

Read issuedinvoices

Identifypayments

Issuereceipts

Findpayments

due

Receipts

Issuepaymentreminder

Reminders

Invoices Payments

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Control Styles…..

Control models emphasize control flow among subsystems

Two general approaches: Centralized control: a single subsystem (central

controller) has the control responsibility of the entire system; it may defer control to other subsystems but the control must be returned to the central controller

Call-return model (top-down subroutine model) Manager model (applies to concurrent systems, in

which several processes run in parallel)

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..Control Styles….

Two general approaches (continued): Event-based control: each subsystem has control

responsibilities; they respond to events generated by the environment and/or other subsystems

Broadcast models: an event is dispatched to all subsystems

Interrupt-driven models: make use of interrupt handlers; typical to RTS

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..Control Styles...

The call-return control model [Fig. 11.7, SE-7]

Routine 1.2Routine 1.1 Routine 3.2Routine 3.1

Routine 2 Routine 3Routine 1

Mainprogram

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…Control Styles..

Example of a centralized control model: an RTS

[Fig. 11.8, SE-7]

Systemcontroller

Userinterface

Faulthandler

Computationprocesses

Actuatorprocesses

Sensorprocesses

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….Control Styles.

Control model with selective broadcasting [Fig. 11.9, SE-7]

Sub-system1

Event and message handler

Sub-system2

Sub-system3

Sub-system4

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…..Control Styles

Example of interrupt-driven control model [Fig. 11.10, SE-7]

Handler1

Handler2

Handler3

Handler4

Process1

Process2

Process3

Process4

Interrupts

Interruptvector

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Reference Architectures…

A domain-specific architecture is characteristic to a particular application domain; it proposes a common architectural structure that can be used across applications within that particular domain

Note that, generally, in architectural design various design models can (and usually need) be applied in combination

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..Reference Architectures....

Main categories: Generic models: models extracted from real

systems that provide a common architectural framework for new applications within the domain (e.g., compiler design)

Reference models: more abstract models that communicate commonly used domain and design concepts; derived from studying the application domain (e.g., the Open Systems Interconnection [OSI] reference model)

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..Reference Architectures.

Generic repository model of a language processing system [Fig. 13.13, SE-7]

Syntaxanalyser

Lexicalanalyser

Semanticanalyser

Abstractsyntax tree

Grammardefinition

Symboltable

Outputdefinition

Pretty-printer

Editor

Optimizer

Codegenerator

Repository

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…Reference Architectures

Example of reference architecture: the OSI model [Fig. 11.11, SE-7]

Application

Presentation

Session

Transport

Network

Data link

Physical

7

6

5

4

3

2

1

Communica tions medium

Network

Data link

Physical

Application

Presentation

Session

Transport

Network

Data link

Physical