Transcript CH12 - Computer and Information Science

Chapter 12
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Client/Server Systems
Database Systems: Design, Implementation, and Management
4th Edition
Peter Rob & Carlos Coronel
What Is Client/Server Computing?
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 Client/server is a term used to describe a computing model
for the development of computerized systems. This model
is based on the distribution of functions between two types
of independent and autonomous processes; servers and
clients.
A client is any process that requests specific services from
server processes. A server is a process that provides
requested services for clients. Both clients and servers can
reside in the same computer or in different computers
connected by a network.
 The key to client/server power is where the requested
processing takes place.

In mainframe systems, all processing takes place on the
mainframe, and the terminal is used to display the data
screens.
 The client/server environment provides a clear separation of
server and client processes.
A Basic Client/Server Computing Model
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Figure 12.1
The Forces That Drive C/S Systems
 The Changing Business Environment
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Global market dynamics and competitive pressure
 Need for fast, efficient, and widespread data access
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 The Need for Enterprise Data Access
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Need for fast, on-demand data access by decision
makers through easy-to-use interfaces
 Rapidly increasing Internet enabled access to external
data through the Internet’s inherent client/server
structure
 End User Productivity Gains Based on the Use of
Data Resources
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End user demand for better ad hoc data access and
data manipulation, better user interfaces, and better
computer integration
The Forces That Drive C/S Systems
 Technological Advances
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Microprocessor Technology
Data Communication and the Internet
Database Systems
Operating Systems and Graphical User Interfaces
(GUIs)
Sophisticated PC-Based End User Application Software
 Cost/Performance Advantages of the PC-Based
Platform

Widespread use of business applications such as word
processing, spreadsheets, DBMS, and desktop
publishing
 New application development languages such as Java
 Internet (Web)-based application development
The Evolution of Client/Server IS
 Mainframes in the 1970s
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Complex, proprietary OS
Dumb terminals
Restricted access
Hardware and software dictated IS
Centralized, complex MIS department
bureaucracy
 Microcomputers in the 1980s
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Easy-to-use software (e.g., spreadsheet)
Micro-based database systems
Data still in mainframes
“Manual download”
The Evolution of Client/Server IS
 Intelligent Terminals
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PCs connected to the mainframe
Electronic download
Proliferation of snapshot versions of corporate DB
Islands of information
Sneaker net
 Local Area Network
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Network operating systems (NOS)
 Powerful PCs
 Common platform for both end users and MIS
specialists
The Evolution of Client/Server IS
 Computer Landscape of the 1990s
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
Networks tie large numbers of heterogeneous
computers
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PC as the common end user station and the point
of access to the entire corporate database
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Advanced applications for direct data access
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The Internet - Network of networks
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Figure 12.2 The Evolution Of The Computing Environment
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Table 12.1 Contrasting Mainframe and Client/Server
Information Systems
Managerial Expectations of C/S Systems
 Client/Server Benefits
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Platform-independent system development
Optimized distribution of processing activities among
different platforms
Use of user friendly, cost effective, and compatible
techniques, methodologies, and specialized tools
 Observations

Client/Server computing is a tool, not the goal.
 Client/Server computing is not the answer to all data
management problems.
 Client/Server computing has its own set of
management problems.
Managerial Expectations of C/S Systems
 MIS Expectations of Client/Server Benefits
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Reduced development and implementation costs
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Reduced development time and increased programmer
productivity
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Extended system life cycle through scalability and
portability
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Reduced system operational cost
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Change of MIS function from development to end user
support
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Enhanced information deployment
Managerial Expectations of C/S Systems
 Organizational Expectations of Client/Server Benefits
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Flexibility and adaptability
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Improved employee productivity
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Improved company work flow and a way to reengineer
business operations
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New opportunities to provide competitive advantages
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Increased customer service satisfaction
Client/Server Architecture
 Three Components of Client/Server Architecture
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The client is any computer process that requests
services from the server. It is also known as the frontend application.
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The server is any computer process providing services
to the clients. The server is also known as the back-end
application.
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The communication middleware is any computer
process(es) through which clients and servers
communicate. It is also known as middleware or
communications layer.
How Client And Server Components Interact
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Figure 12.3
An Example Of Client/Server Architecture
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Figure 12.4
Client/Server Architecture
 Client/Server Principles
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Hardware independence
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Software independence
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Operating systems
Network systems
Applications
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Open access to services
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Process distribution
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Process autonomy
Maximization of local resources
Scalability and flexibility
Interoperability and integration
Standards
Client/Server Architecture
 Client Components
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Powerful hardware
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An operating system capable of multitasking
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A graphical user interface (GUI)
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Communications capability
Client Components
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Figure 12.5
Client/Server Architecture
 Server Components
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File services
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Print services
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Fax services
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Communications services
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Database services
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Transaction services
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Miscellaneous services
Server Components
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Figure 12.6
Client/Server Architecture
 Characteristics of Server Hardware
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Fast CPU
Fault-tolerant capabilities
Expandability of CPU, memory, disk, and peripherals
Bus support for multiple add-on boards
Multiple communications options
 Server Process Benefits from the
Client/Server Architectural Principles
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Location independence
 Resource optimization
 Scalability
 Interoperability and integration
Client/Server Architecture
 Communications Middleware Components
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The use of database middleware yields
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Network independence
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Database server independence
Two levels of communications middleware
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The physical level deals with the communications
between client and server computers (computer to
computer).
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The logical level deals with the communications
between client and server processes (process to
process).
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Table 12.2 The OSI Network Reference Model
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Figure 12.7 Information Flow Through The OSI Model
Transport Process ID
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Figure 12.8
Client/Server Architecture
 Network Protocols
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Transmission Control Protocol/Internet Protocol
(TCP/IP)
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Internetwork Packet Exchange/ Sequenced Packet
Exchange (IPX/SPX)
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Developed by Novell for LAN communications
Supported by the majority of client/server network
applications and major PC operating systems
Network Basic Input Output System (NetBIOS)
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Official communication protocol of the Internet
Developed by IBM for PC applications communications
Supported by the majority of PC operating systems and
applications
Application Program to Program Communications
(APPC)
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Used in IBM mainframe Systems Network Architecture
(SNA) environments
Client/Server Architecture
 Database Middleware Components
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Application programming interface (API)
interfaces with the client application.
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The database translator translates the SQL
requests into the specific database server syntax.
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The network translator manages the network
communications protocols.
 Three Main Benefits of Using Middleware
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Access multiple databases
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Database server-independent
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Network protocol-independent
Database Middleware Components
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Figure 12.9
Interaction Between Client/Server Middleware Components
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Figure 12.10
Middleware Accessing Multiple Database Servers
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Figure 12.11
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Client/Server Architecture
 Middleware Classifications
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Messaging-oriented middleware (MOM)
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Remote-procedure-call-based (RPC-based) middle
ware
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Object-based middleware
The Quest for Standards
 Standard-Setting Organizations
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IEEE (Institute of Electrical and Electronics
Engineers)
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ANSI (American National Standards Institute)
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Network and hardware
Programming languages (e.g., COBOL, SQL)
ISO (International Standards Organization)
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OSI (Open Systems Interconnection) reference
The Quest for Standards
 Competing Standards
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Client operating systems
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Client graphical user interfaces
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Microsoft Windows 96/98/2000 -- De facto standard
OS/2 Presentation Manager, Macintosh, UNIX (e.g., Notif,
OpenLook)
Server operating systems and network protocols
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Microsoft Windows 96/98/2000 -- De facto standard
OS/2, Apple’s Mac OS 8.5, Unix including Linux
Database servers: Unix, OS/2, Windows NT Server/2000
Server
Printer and file servers: Novel Netware
LAN protocols: TCP/IP, IPX/SPX, NetBIOS
Middleware
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ODBC, IDAPI, DRDA, Q+E
Client/Server Options
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Figure 12.13
Client/Server Databases
 Functions of the Client/Server Database
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Provide transparent data access to multiple and
heterogeneous clients regardless of the hardware,
software, and network platform.
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Allow client requests to the database server over
the network.
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Process client data requests at the local server.
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Send only the SQL results to the clients over the
network.
Client/Server Databases
 Characteristics of Distributed Client/Server
Database Systems
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The location of data is transparent to the user.
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Data can be accessed and manipulated by the end
user at any time and in many ways.
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The processing of data is distributed among
multiple computers.
Client/Server Architectural Styles
 Two Key Questions for the Client/Server Architecture
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How is the division made?
Where in the system should the results of that division
be placed?
 Three Application Logic Components
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Input/Output (I/O)
Processing
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I/O processing logic
Application or business logic
Data management logic
Storage
Application Logic Components
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Figure 12.14
Client/Server Architectural Styles
 Five Functional Logic Components
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Presentation logic
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I/O processing logic
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Application of business logic
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Data management logic
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Data manipulation logic
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Figure 12.15 Application Functional Logic Components
Client/Server Architectural Styles
 Typical Logic Component Placement
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The presentation logic is always placed on the client
side.
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The I/O processing logic may be placed on the client
side or on the server side, but more commonly on the
client side.
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The business logic can also go either to the client or
the server, but usually on the client side.
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The data management logic can also be placed on
either the client or the server side, but normally on the
client side as part of the application code.
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The data manipulation logic is most commonly located
on the server side.
Functional Logic Splitting In Four Client/Server
Architectural Styles
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Figure 12.16
Client/Server Architectural Styles
 Notes on Figure 12.16
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The file server architectural style reflects a setup in
which the client does most of the processing, whereas
the server side only manages the data storage and
retrieval.
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The data management logic is split between the client
and the server computers in the database server
architectural style.
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The transaction server architectural style permits the
sharing of transaction details between the client and
the server.
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The application server architecture makes it possible to
enjoy the benefits of client/server computing even
when the client computers are not powerful enough to
run some of the client/server applications.
Client/Server Implementation Issues
 Client/Server versus Traditional Data Processing
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Major changes brought by client/server computing
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From proprietary to open systems
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From maintenance-oriented coding to analysis,
design, and service
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From data collection to data deployment
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From a centralized to a more distributed style of
data management
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From vertical, inflexible to more horizontal, flexible
organizational style
Client/Server Implementation Issues
 Changes in the DP Environment Brought by
Client/Server Computing
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Hardware
Single-vendor-dependent  Integration of different
hardware platforms
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Software
Mainframe, 3GL  GUI, networks, communications
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Data
Centralized, single repository  Distributed, multiple
formats
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Procedures
Centralized, rigid, complex  Flexible, decentralized
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People
Requires support and training for new skills and
technology
Client/Server Implementation Issues
 Managerial Considerations
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Management and support of communications
infrastructure
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Management and support of applications
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Controlling escalating and hidden costs
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Managing people and cultural changes
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Managing multiple vendor relationships
Client/Server Implementation Issues
 Client/Server Development Tools
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GUI-based development
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A GUI builder that supports multiple interfaces
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Object-oriented development with support for
code reusability
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Data dictionary with a central repository for data
and applications
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Support for multiple databases
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Data access regardless of data model
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Seamless access to multiple databases
Client/Server Implementation Issues
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Complete SDLC support from planning to
implementation and maintenance
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Team development support
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Support for third-party development tools
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Prototyping and rapid application development
(RAD) capabilities
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Support for multiple platforms
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Support for middleware protocols
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Multiple network support
Client/Server Implementation Issues
 An Integrated Approach
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Six Phases of Client/Server Decision
1. Information systems infrastructure self-study
2. Client/Server infrastructure definition
3. Selecting a window of opportunity
4. Management commitment
5. Implementation
6. Review and evaluation