ClientServer Systems

1
Chapter 12

• Client/Server Systems
• Database Systems Design, Implementation, and
  Management, Fifth Edition, Rob and Coronel

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In this chapter, you will learn

• What client/server computing is
• What the advantages of using client/server
  systems are
• How client/server systems evolved
• About client/server systems components and how
  they interact
• What effect the client/server system has on the
  DBMS
• How client/server systems might be introduced
  into an organization
• What factors affect the implementation of
  client/server systems

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Client/Server Computing

• Computing model for the development of
  computerized systems
• Client requests specific service
• Server provides requested service
• Reside on same or different computers

Figure 12.1
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Client/Server Computing (cont.)

• Key to client server power is where request
  processing takes place
• Extent of sharing processing
• Thin client
• Thin server
• Fat client
• Fat server
• Classification
• 2-tier
• 3-tier

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Forces that Drive Client/Server Trend

• Changing business environment
• Growing need for enterprise data access
• Demand for end-user productivity gains based on
  efficient use of data
• Technological advances
• Growing cost/performance advantages

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Evolution of Computing Environment
Figure 12.2
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Mainframe vs. Client/Server Systems
Table 12.1
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Managerial Expectations of Client/Server Systems

• Client/Server efficiency functions
• Platform independent development
• Optimized distribution of processing activities
  among different platforms
• User friendly and cost effective techniques,
  methodologies, and specialized tools
• Observations
• Tool, not end goal
• Not answer to all data management problems
• Has own set of management problems

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MIS Expectations of Client/Server Benefits

• Reduced development and implementation costs
• Reduced development time and increased programmer
  productivity
• Extended system life cycle through scalability
  and portability
• Reduced system operational cost
• Change of MIS function from development to
  end-user support
• Enhanced information deployment

10
Organizational Expectations of Client/Server
Benefits

• Flexibility and adaptability
• Improved employee productivity
• Improved company work flow and way to reengineer
  business operations
• New opportunities for competitive advantages
• Increased customer service satisfaction

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Components of Client/Server Architecture

• Client
• Front-end application
• Server
• Back-end application
• Communications middleware
• Communications layer

Figure 12.3
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Example Client/Server Architecture
Figure 12.4
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Client/Server Principles

• Hardware independence
• Software independence
• Operating systems
• Network systems
• Applications
• Open access to services
• Process distribution
• Process autonomy
• Maximization of local resources
• Scalability and flexibility
• Interoperability and integration
• Standards

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Client Components
Figure 12.5
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Server Components

• File services
• Print services
• Fax services
• Communications services
• Database services
• Transaction services
• Miscellaneous services

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Server Components
Figure 12.6
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Typical Characteristics of Server Hardware

• Fast CPU
• Fault-tolerant capabilities
• Dual power
• Standby power
• Error checking and correcting memory
• RAID
• Expandability of CPU, memory, disk, and
  peripherals
• Bus support for multiple add-on boards
• Multiple communications options

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Server Process Benefits

• Location independence
• Resource optimization
• Scalability
• Interoperability and integration

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Database Middleware

• Network independence
• Front-end application accesses data without
  regard to network protocols
• Database server independence
• Generic SQL to access different database servers
• Isolates programmer from SQL dialect differences

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Communications Middleware

• Two levels
• Physical level
• Client and server computers
• Logical level
• Client and server processes
• Interprocess communication (ICP) protocols

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OSI Network Reference Model
Table 12.2
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Information Flow through OSI Model
Figure 12.7
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Transport Process ID
Figure 12.8
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Network Protocols

• Transmission Control Protocol/Internet Protocol
  (TCP/IP)
• Internetwork Packet Exchange/ Sequenced Packet
  Exchange (IPX/SPX)
• Network Basic Input Output System (NetBIOS)
• Application Program to Program Communications
  (APPC)

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Database Middleware Components
Figure 12.9
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Interactions between Middleware Components
Figure 12.10
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Middleware Accessing Multiple Database Servers
Figure 12.11
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Middleware Accessing Mainframe Databases
Figure 12.12
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Middleware Classifications

• Messaging-oriented middleware (MOM)
• Remote-procedure-call-based (RPC-based) middle
  ware
• Object-based middleware

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Competing Standards

• Client operating systems
• Microsoft Windows
• OS/2, Apple Mac OS, Unix, Linux
• Client graphical user interfaces
• Microsoft Windows
• OS/2 Presentation Manager, Macintosh, UNIX
• Server operating systems and network protocols
• Database servers Unix, OS/2, Windows NT
  Server/2000 Server
• Printer and file servers Novell Netware
• LAN protocols TCP/IP, IPX/SPX, NetBIOS
• Middleware
• ODBC, IDAPI, DRDA, QE

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Client/Server DBMS Functions

• Transparent data access to multiple,
  heterogeneous clients
• Allow client requests to the database server over
  network
• Process client data requests at local server
• Send only SQL results to clients over network

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Application Logic Components
Figure 12.14
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Client/Server Architectural Styles

• Two Key Questions
• How is the division made?
• Where should the results of division be placed?
• Five Functional Logic Components
• Presentation logic
• I/O processing logic
• Application of business logic
• Data management logic
• Data manipulation logic

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Application Functional Components
Figure 12.15
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Functional Logic Splitting
Figure 12.16
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Client/Server versus Traditional DP

• Proprietary to open systems
• Maintenance-oriented coding to analysis, design,
  and service
• Data collection to data deployment
• Centralized to distributed style
• Vertical, inflexible to horizontal, flexible
  organizational style
• Differences in IS components

37
Client/Server Implementation Issues

• Management Issues
• Communications infrastructure
• Applications
• Controlling escalating and hidden costs
• People and cultural changes
• Multiple vendor relationships
• Development tool acquisition
• Determination if client/server approach is
  correct