CLIENT SERVER SYSTEM

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CLIENT / SERVER SYSTEM
What Is a Client/Server system? A system that
links a client and server through networks. It
describes 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.
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Client / Server System
Network
Server process
Client process
Clients request services from different server
processes.
Services File, print, fax, multimedia,
communications
Clients can request services from several servers
and servers can provide services for more than
one clients.
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Forces that drive the trend to Client/Server
Systems

• The changing business environment.
• The growing need for enterprise data access.
• The demand for end user productivity gains based
  on the efficient use of data resources.
• Technological advances that have made
  clients/server computing practical.
• Growing cost/performance advantages of PC-based
  platforms.
• Cost / Performance advantages of the PC-based
  platform

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Driving forces

• Technological Advances
• -Microprocessor Technology New microprocessors
  are capable to, or even better than, that of many
  mainframes and minicomputer systems. Such
  processing power makes it possible to dedicate
  PCs to tasks that used to be delegated to
  mainframes and minicomputers.
• - Data Communications and Internet Advances in
  data communication and the Internet have allowed
  the integration of PCs with the existing networks
  of minicomputers and mainframes.

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Driving forces -cont.
Operating Systems and Graphical User Interfaces
(GUI) The GUI made it possible for end users to
put this power to work, thus making the GUI a
major contributing factor to the PCs success in
the workplace.The GUI has made it possible for
end users to create many of their own
applications, thus making them more autonomous.
Ex) Microsoft Windows, Apples Macintosh, IBMs
OS/2
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Client/Server v.s. Mainframes
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Client/Server Architecture
The client/Server architecture is based upon
hardware and software components that interact to
form a system. Front-end application(Client)
Any computer process that requests services from
the server. Back-end application(Server) Any
computer processing providing services to the
clients. Communications middleware(Middleware)
Any computer process through which clients and
servers communicate.
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How components interact?
SQL
SQL
Client process
Communications middleware network
Database server
Data
Data
Clients process sends SQL request through
communications middleware.
Middleware routes SQL request to database server
process.
Database server process receives request,
validates it, and executes it.
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Client/server principles
The client/server architectures components must
conform to some basic principles if they are to
interact properly. Principles -Hardware
independence Client, server, and middleware must
run on multiple hardware platforms. -Software
independence All components must support
multiple OS, multiple network protocols, multiple
applications Exgt Windows,
Linux, IPX, TCP/IP -Open access to service All
clients in the system must have open access to
all the services provided within the networks,
and these services must not be dependent on the
location of the clients or the servers.
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Client/server principles -cont.
-Process distribution A prime identifying
characteristic of client/server system is that
the processing of information is distributed
among clients and servers. The server process
must be shard among all clients to best utilize
all resources. Scalability and flexibility
requires that the client and server processes be
easily upgradable to run on more powerful
hardware and software platforms. -Standards
Standards ensure that all components interact in
an orderly manner to achieve the desired result.
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Client Component
Desirable client hardware and software
features - Powerful Hardware -An operating
system capable of multitasking -A graphical
user interface( GUI ) -Communications
capabilities
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Server components
Servers typically provide -File services A
client connected to the network can store files
on the file server as if it were another local
hard disk. -Print services A client can access
any one of the printers as if it were directly
connected to its own computers -Fax services The
client PC submit the data to be faxed to the fax
server with the required information such as a
fax number and fax server transmit the
fax. -Communication services let client PCs
connected to the communications server access
other host computers or services to which the
client is not directly connected.
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Server components cont.
-Database services When server receives the SQL
codes, it validates it, executes it, and sends
only the results to the client. The computer
that houses the server process should be a more
powerful computer than the average client
computer because it must be able to handle
multiple requests from multiple clients. Minimum
requirements -Fast CPU (RISC, Pentium,
PowerPC) -Fault-tolerant capability -Expendability
of CPU -Multiple communications options
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Communications middleware components
If the same application is to be used with a
different database and network, the applications
routines must be rewritten for the new database
and network protocols. - This is where middleware
comes in handy. The use of middleware
yields, Network independence by allowing
front-end application to access data without
regard to the network protocols. Database server
independence by allowing front-end user to
request from multiple database servers with
different SQL codes.
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Communications middleware components
Communications middleware operates at two
levels, The physical layer It address how the
computers are physically linked. The physical
links include network software and hardware. The
software include the network protocols.
Physically, the communication middleware is the
network. The logical layer It deals with how the
client and server processes communication. The
logical characteristics are governed by
process-to-process communication protocols that
give the signals meaning or purpose.
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Communications middleware components
Open Systems Interconnection (OSI) network
reference model
Application - Presentation - Session - Transport
- Network - Data-link - Physical The application
and presentation layers provide end user
application-oriented functions. The session layer
ensures and controls program-to-program
communications. The transport, network,
data-link, and physical layers provide
network-oriented functions.
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Network protocols
Network protocol is a set of rules that
determines how messages between computers are
sent, interpreted, and processed. As a result of
the client/server computing boom, many mainframes
and midrange computers are now implementing
support for more open, nonproprietary network
standards such as TCP/IP, to allow direct access
from client/server PC-based front-end
applications. The selection of network topology
and protocols is one of the most critical
decisions in a client/server systems
development. For the commercial software
developers, this may be market-driven. Because
this will decide the number of people they can
reach.
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Network Protocols
Transmission Control Protocol/ Internet
Protocol (TCP/IP) The official communications
protocol of the Internet. TCP/IP is the main
communications protocol used by Unix systems, is
supported by most operating systems at the
midrange and personal computer levels.
Internet Packet Exchange/Sequenced Packet
Exchange (IPX/SPX) Communications protocol
developed by Novell. IPX/SPX is supported by the
majority of client/server network applications
and by all PC operating systems.
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Database middleware components
Middleware software is divided into three main
components -Applications programming interface
(API) Middleware allows the client process to
be database-server-independent. -Database
translator Translate the SQL requests into
the specific database server syntax. -Network
translator Manages the network
communications protocols.
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Database middleware components
Client front-end
Database middleware
Network protocol
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Major changes from traditional data processing
From proprietary to open system From
maintenance-oriented coding to analysis, design,
and service From data collection to data
development From a centralized to a more
distributed style of data management From
vertical, inflexible organizational style to a
more horizontal, flexible organizational style
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Implementation of client/server systems

The implementation of client/server systems
represents a big change for any organization. The
change reflects both basic information access
philosophy and considerable technological shifts,
the MIS department in particular must work to
adapt to a change from a traditional
data-processing style to a client/server
data-processing style. A gradual and progressive
plan must be implemented by the MIS department.