Transcript Systems Analysis and Design 9th Edition

Systems Analysis and Design
9th Edition
Chapter 10
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
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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 companywide 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 fileoriented 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.
2.
3.
4.
5.
6.
Management summary
System components
System environment
Implementation requirements
Time and cost estimates
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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