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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
Database Systems: Design, Implementation, & Management,
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Edition, Rob & Coronel
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Client/Server Computing (con’t.)
• 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 enduser support
• Enhanced information deployment
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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
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel
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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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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Interactions between
Middleware Components
Figure 12.10
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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, Q+E
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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
–
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–
–
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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
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Client/Server Implementation Issues
• Management Issues
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–
–
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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
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