Systems Analysis and Design 8th Edition

Chapter 10System Architecture

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)

• Faster response, better customer service, and lower costs

• 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 (page 458)– 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– Availability– Security

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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 – Collective knowledge

– Internet operating system, sharing resources

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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 (page 471)– The OSI model consists of seven conceptual layers– Each layer performs a specific function– Offers a set of design standards

• Network Modeling Tools– As you translate the OSI logical model into a

physical model of the networked system, you can use software tools, such as Microsoft Visio

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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)– Manages data flow

between connected devicesw

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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

• Routers– Routers differ from

switches in that they work at OSI level 3 (IP packets)

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

– Proxy server• Connects internal LAN

clients to Internet

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Network Models

• Network Protocols– The network must use a protocol– A popular network protocol is Transmission

Control Protocol/Internet Protocol (TCP/IP)– A familiar example of a TCP/IP protocol is the file

transfer protocol (FTP)• Network Licensing Issues– When considering a network design, it is

important to take into account 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)– Versions or amendments to improve bandwidth,

range and security – Mbps (megabits per second)

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Wireless Networks

• Wireless Network Standards

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Wireless Networks

• Wireless Network Topologies (pgs. 477-478)– 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 (close acces, low power)– On addition to 802.11 protocols for LANs, IEEE is

working on 802.16 standards (30 mile range) called:

– MANs (metropolitan area networks)– WirelessMAN™ - WiMAX

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Systems Design Completion

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

structure similar to the following:• Executive summary• System components• System environment• Implementation requirements• Time and cost estimates• Appendices

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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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