Systems Analysis and Design 8 Edition

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Oct 23, 2013 (4 years and 20 days ago)

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Systems Analysis and Design
8
th

Edition

Chapter 9

System 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

2

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

3

Chapter Objectives


Explain network protocols and licensing issues


Describe wireless networking, including
wireless standards, topologies, and trends


Describe the system design specification

4

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

5

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


6

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

7

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

8

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

9

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

10

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


11

Planning the Architecture


Servers


Server


Clients


Mainframe architecture


Server
-
based processing


12

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

13

Planning the Architecture


Clients


Stand
-
Alone Computing


Local and wide area
networks


Client
-
based processing


14

Client/Server Architecture


Overview

15

Client/Server Architecture


Client/Server Design Styles

16

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

17

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

18

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

19

Internet
-
Based Architecture


Developing E
-
Commerce Solutions In
-
House

20

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

21

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

22

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

23

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

24

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

25

Processing Methods


Combined Online and Batch Processing

26

Network Models


The OSI (
Objective Systems Integrators
) Reference Model


The OSI model consists of seven 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

27

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

28

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


29

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)

30

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


31

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

32

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

33

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)

34

Wireless Networks


Wireless Network Standards

35

Wireless Networks


Wireless Trends


Wi
-
Fi


BlueTooth


On addition to 802.11 protocols for LANs, IEEE is
working on 802.16 standards


MANs (metropolitan area networks)


WirelessMAN

-

WiMAX

36

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

37

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

38

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

39

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

40

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

41

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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