Systems Analysis and Design 9th Edition

Chapter 10System Architecture

Chapter Objectives

• Provide a checklist of issues to consider when selecting a system architecture

• Describe servers, server-based processing, clients, and client-based processing

• Explain client/server architecture, including tiers, cost-benefit issues, and performance

• Compare in-house e-commerce development with packaged solutions

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Chapter Objectives

• Discuss the potential impact of cloud computing and Web 2.0

• Explain the difference between online and batch processing

• Define network topology, including hierarchical, bus, ring, and star models

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Chapter Objectives

• Explain network protocols and licensing issues• Describe wireless networking, including

wireless standards, topologies, and trends• Describe the system design specification

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Introduction

• An effective system combines elements into an architecture, or design, that is flexible, cost-effective, technically sound, and able to support the information needs of the business

• System architecture translates the logical design of an information system into a physical structure that includes hardware, software, network support, and processing methods

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System Architecture Checklist

• Enterprise Resource Planning (ERP)– The objective of ERP is to establish a company-

wide strategy for using IT resources– Supply chain management (SCM)

• Initial Cost and TCO– During the final design stage, you make decisions

that will have a major impact on the initial costs and TCO for the new system

– You should review all previous cost estimates

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System Architecture Checklist

• Scalability– Scalability, also called extensibility, refers to a

system’s ability to expand, change or downsize easily to meet the changing need of a business enterprise

– Especially important in implementing systems that are volume-rated, such as transaction processing systems

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System Architecture Checklist

• Web Integration– An information system

includes applications – Web-centric architecture – Avoids many of the

connectivity and compatibility problems that typically arise

– E-marketplaces

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System Architecture Checklist

• Legacy System Interface Requirements– The new system might have to interface with one

or more legacy systems– Interfacing a new system with a legacy system

involves analysis of data formats and compatibility– The analyst must know if the new application

eventually will replace the legacy system

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System Architecture Checklist

• Processing Options– In planning the architecture, designers also must

consider how the system will process data - online or in batches

– Provision must be made for backup and speedy recovery in the event of system failure

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System Architecture Checklist

• Security Issues– Security threats and

defenses are a major concern to a systems analyst

– The analyst must consider security issues that relate to system design specifications

– Web-based systems introduce additional security concerns

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Planning the Architecture

• Servers– Server– Clients– Mainframe architecture– Server-based processing

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Planning the Architecture

• Clients– As PC technology exploded in the mid-1980s and

1990s, powerful microcomputers quickly appeared on corporate desktops

– Users found that they could run their own word processing, spreadsheet, and database applications

– Companies linked the stand-alone computers into networks

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Planning the Architecture

• Clients– Stand-Alone Computing– Local and wide area

networks– Client-based processing

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Client/Server Architecture

• Overview

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Client/Server Architecture

• Client/Server Design Styles

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Client/Server Architecture

• Fat and Thin Clients

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Client/Server Architecture

• Client/Server Tiers– Two-tier design– Three-tier design

• Middleware– Enables the tiers to communicate and pass data

back and forth– Provides a transparent interface– Can integrate legacy systems and Web-based

applications

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Client/Server Architecture

• Cost-Benefit Issues– Client/server systems enable the firm to scale the

system in a rapidly changing environment– Client/server computing also allows companies to

transfer applications from expensive mainframes to less expensive client platforms

– Client/server systems reduce network load and improve response times

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Client/Server Architecture

• Client/Server Performance Issues– In contrast to the centralized system, a client/server

design separates applications and data– Distributed database management system (DDBMS)– The system is scalable, so new data sites can be

added without reworking the system design– The system is less likely to experience catastrophic

failure

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Internet-Based Architecture

• Developing E-Commerce Solutions In-House

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Internet-Based Architecture

• Packaged Solutions and E-commerce Service Providers– Many vendors offer turnkey systems for

companies – Another alternative is to use an application service

provider (ASP)– Another option is managed hosting– Consider the experience of other companies in the

same industry

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Internet-Based Architecture

• Corporate Portals– A corporate portal can

provide access for customers, employees, suppliers, and the public

• Cloud Computing– Effectively eliminates

compatibility issues– Scaling on demand– Requires significantly

more bandwidth

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Internet-Based Architecture

• Web 2.0– Envisions a second

generation of the web that will enable people to collaborate, interact, and share information more dynamically

– Wiki– Internet operating

system

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Processing Methods

• Online Processing– Because it is interactive,

online processing avoids delays and allows a constant dialog between the user and the system

– Online processing also can be used with file-oriented systems

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Processing Methods

• Batch Processing– The IT operations group can run batch programs

on a predetermined schedule, without user involvement, during regular business hours, at night, or on weekends

– Require significantly fewer network resources than online systems

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Processing Methods

• Combined Online and Batch Processing

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Network Models

• The OSI Reference Model– The OSI model consists

of seven layers– Each layer performs a

specific function– Offers a set of design

standards

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Network Models

• Network Protocols– In all cases, the network must use a protocol– Transmission Control Protocol/Internet Protocol

(TCP/IP)– File Transfer Protocol (FTP)

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Network Models

• Network Topology– Hierarchical network

• it mirrors the actual operational flow in the organization

• One disadvantage of a hierarchical network is that if a business adds additional processing levels, the network becomes more complex and expensive to operate and maintain

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Network Models

• Network Topology– Bus network

• Devices can be attached or detached from the network at any point without disturbing the rest of the network

• Overall performance declines as more users and devices are added

• Today, the bus design is much less popular

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Network Models

• Network Topology– Ring network

• One disadvantage of a ring network is that if a network device fails (such as a PC or a server), the devices downstream from the failed device cannot communicate with the network

• Multistation Access Unit (MAU)

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Network Models

• Network Topology– Star network

• Disadvantage of the star design is that the entire network is dependent on the switch

• However, in most large star networks, backup switches are available immediately in case of hardware failure

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Network Models

• Network Topology– Mesh network

• While this design is extremely reliable, it also is very expensive to install and maintain

• Originally developed for military applications

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Network Models

• Routers– Routers differ from

switches in that they work at a higher OSI level

– Can connect to a larger, dissimilar network, such as the Internet

– Gateway– Proxy server

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Network Models

• Network Modeling Tools– As you translate the OSI

logical model into a physical model of the networked system, you can use software tools

• Network Licensing Issues– Software licensing

restrictions

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Wireless Networks

• A wireless local area network, or WLAN• Wireless Network Standards– 802.11– Institute of Electrical and Electronics Engineers

(IEEE)– Amendments– Mbps (megabits per second)

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Wireless Networks

• Wireless Network Standards– 802.11g– 802.11n– Multiple input/multiple output (MIMO)– Multipath design– 802.11y

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Wireless Networks

• Wireless Network Topologies– Basic Service Set (BSS) – infrastructure mode– Access point– Extended Service Set (ESS)– Roaming– Independence Service Set (ISS) – peer-to-peer

mode

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Wireless Networks

• Wireless Trends– Wi-Fi Alliance– Wi-Fi (wireless fidelity)– BlueTooth– On addition to 802.11 protocols for LANs, IEEE is

working on 802.16 standards– MANs (metropolitan area networks)– WiMAX

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Systems Design Completion

• System Design Specification– A typical system design specification uses a

structure similar to the following:1. Management summary2. System components3. System environment4. Implementation requirements5. Time and cost estimates6. Additional material

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Systems Design Completion

• User Approval– Users must review and approve the interface design,

report and menu designs, data entry screens, source documents, and other areas of the system that affect them

– Other IT department members also need to review the system design specification

– When the system design specification is complete, you distribute the document to a target group of users, IT department personnel, and company management

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Systems Design Completion

• Presentations– The first presentation is to the systems analysts,

programmers, and technical support staff members – Your next presentation is to department managers

and users from departments affected by the system– The final presentation is for company management– Management might reach one of three decisions:

proceed with systems development, perform additional work on the systems design phase, or terminate the project

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Chapter Summary

• An information system combines hardware, software, data, procedures, and people into a system architecture

• The analyst must consider enterprise resource planning, initial cost and TCO, scalability, Web integration, legacy interface requirements, processing options, and security issues

• An architecture requires servers and clients

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Chapter Summary

• Compared to file server designs, client/server systems are more scalable and flexible

• In implementing a design, an analyst should consider e-commerce strategies, the availability of packaged solutions, and corporate portals, which are entrances to a multifunction Web site

• The primary processing methods are online and batch processing

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Chapter Summary

• Networks allow the sharing of hardware, software, and data resources in order to reduce expenses and provide more capability to users

• The way a network is configured is called the network topology

• The system design specification presents the complete systems design for an information system

• Chapter 10 complete

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