Chapter 10

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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• 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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• 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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• 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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• 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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• 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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• 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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• 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 Design Styles

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• Fat and Thin Clients

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• 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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• 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 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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• 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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• 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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• 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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• 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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• 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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