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Transcript of Client Server Systems
Client/Server Systems
Rosemarie N. PaglicawanAlbert Macapugay
Ricky PalmedaMSIT
What Is Client/Server Computing? 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
The Forces That Drive C/S Systems
The Changing Business Environment Global market dynamics and competitive pressure Need for fast, efficient, and widespread data access
The Need for Enterprise Data Access 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 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 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
Complex, proprietary OS Dumb terminals Restricted access Hardware and software dictated IS Centralized, complex MIS department bureaucracy
Microcomputers in the 1980s 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
PCs connected to the mainframe Electronic download Proliferation of snapshot versions of corporate DB Islands of information Sneaker net
Local Area Network 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
Networks tie large numbers of heterogeneous computers
PC as the common end user station and the point of access to the entire corporate database
Advanced applications for direct data access The Internet - Network of networks
The Evolution Of The Computing Environment
Contrasting Mainframe and Client/Server Information Systems
Managerial Expectations of C/S Systems
Client/Server Benefits 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 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
Managerial Expectations of C/S Systems
Organizational Expectations of Client/Server Benefits Flexibility and adaptability
Improved employee productivity
Improved company work flow and a way to reengineer business operations
New opportunities to provide competitive advantages
Increased customer service satisfaction
Client/Server Architecture Three Components of Client/Server
Architecture The client is any computer process that requests services
from the server. It is also known as the front-end application.
The server is any computer process providing services to the clients. The server is also known as the back-end application.
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
An Example Of Client/Server Architecture
Client/Server Architecture 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
Client/Server Architecture Client Components
Powerful hardware
An operating system capable of multitasking A graphical user interface (GUI)
Communications capability
Client Components
Client/Server Architecture Server Components
File services
Print services Fax services
Communications services
Database services Transaction services
Miscellaneous services
Server Components
Client/Server Architecture Characteristics of Server Hardware
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 Location independence Resource optimization Scalability Interoperability and integration
Client/Server Architecture Communications Middleware Components
The use of database middleware yields○ Network independence○ Database server independence
Two levels of communications middleware○ The physical level deals with the communications
between client and server computers (computer to computer).
○ The logical level deals with the communications between client and server processes (process to process).
The OSI Network Reference Model
Information Flow Through The OSI Model
Transport Process ID
Client/Server Architecture Network Protocols
Transmission Control Protocol/Internet Protocol (TCP/IP)○ Official communication protocol of the Internet
Internetwork Packet Exchange/ Sequenced Packet Exchange (IPX/SPX)○ 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)
○ Developed by IBM for PC applications communications
○ Supported by the majority of PC operating systems and applications
Application Program to Program Communications (APPC)○ Used in IBM mainframe Systems Network
Architecture (SNA) environments
Client/Server Architecture Database Middleware Components
Application programming interface (API) interfaces with the client application.
The database translator translates the SQL requests into the specific database server syntax.
The network translator manages the network communications protocols.
Three Main Benefits of Using Middleware Access multiple databases Database server-independent Network protocol-independent
Database Middleware Components
Interaction Between Client/Server Middleware Components
Middleware Accessing Multiple Database Servers
Client/Server Architecture Middleware Classifications
Messaging-oriented middleware (MOM)
Remote-procedure-call-based (RPC-based) middle ware
Object-based middleware
The Quest for Standards Standard-Setting Organizations
IEEE (Institute of Electrical and Electronics Engineers)○ Network and hardware
ANSI (American National Standards Institute)○ Programming languages (e.g., COBOL, SQL)
ISO (International Standards Organization)○ OSI (Open Systems Interconnection) reference
The Quest for Standards Competing Standards
Client operating systems○ Microsoft Windows 96/98/2000 -- De facto standard○ OS/2, Apple’s Mac OS 8.5, Unix including Linux
Client graphical user interfaces○ Microsoft Windows 96/98/2000 -- De facto standard ○ OS/2 Presentation Manager, Macintosh, UNIX (e.g.,
Notif, OpenLook) Server operating systems and network protocols
○ Database servers: Unix, OS/2, Windows NT Server/2000 Server
○ Printer and file servers: Novel Netware○ LAN protocols: TCP/IP, IPX/SPX, NetBIOS
Middleware○ ODBC, IDAPI, DRDA, Q+E
Client/Server Options
Client/Server Databases Functions of the Client/Server Database
Provide transparent data access to multiple and heterogeneous clients regardless of the hardware, software, and network platform.
Allow client requests to the database server over the network.
Process client data requests at the local server.
Send only the SQL results to the clients over the network.
Client/Server Databases Characteristics of Distributed Client/Server
Database Systems The location of data is transparent to the user.
Data can be accessed and manipulated by the end user at any time and in many ways.
The processing of data is distributed among multiple computers.
Client/Server Architectural Styles Two Key Questions for the Client/Server
Architecture How is the division made? Where in the system should the results of that division be placed?
Three Application Logic Components Input/Output (I/O) Processing
○ I/O processing logic○ Application or business logic○ Data management logic
Storage
Application Logic Components
Client/Server Architectural Styles Five Functional Logic Components
Presentation logic
I/O processing logic Application of business logic
Data management logic
Data manipulation logic
Application Functional Logic Components
Client/Server Architectural Styles Typical Logic Component Placement
The presentation logic is always placed on the client side.
The I/O processing logic may be placed on the client side or on the server side, but more commonly on the client side.
The business logic can also go either to the client or the server, but usually on the client side.
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.
The data manipulation logic is most commonly located on the server side.
Functional Logic Splitting In Four Client/Server Architectural Styles
Client/Server Architectural Styles Notes on Figure 12.16
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.
The data management logic is split between the client and the server computers in the database server architectural style.
The transaction server architectural style permits the sharing of transaction details between the client and the server.
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 Major changes brought by client/server computing
○ From proprietary to open systems
○ From maintenance-oriented coding to analysis, design, and service
○ From data collection to data deployment
○ From a centralized to a more distributed style of data management
○ From vertical, inflexible to more horizontal, flexible organizational style
Client/Server Implementation Issues
Changes in the DP Environment Brought by Client/Server Computing Hardware
Single-vendor-dependent Integration of different hardware platforms
SoftwareMainframe, 3GL GUI, networks, communications
DataCentralized, single repository Distributed, multiple formats
ProceduresCentralized, rigid, complex Flexible, decentralized
PeopleRequires support and training for new skills and technology
Client/Server Implementation Issues Managerial Considerations
Management and support of communications infrastructure
Management and support of applications
Controlling escalating and hidden costs
Managing people and cultural changes Managing multiple vendor relationships
Client/Server Implementation Issues Client/Server Development Tools
GUI-based development A GUI builder that supports multiple interfaces Object-oriented development with support for code
reusability Data dictionary with a central repository for data and
applications Support for multiple databases Data access regardless of data model Seamless access to multiple databases
Client/Server Implementation Issues
Complete SDLC support from planning to implementation and maintenance
Team development support
Support for third-party development tools
Prototyping and rapid application development (RAD) capabilities
Support for multiple platforms
Support for middleware protocols Multiple network support
Client/Server Implementation Issues An Integrated Approach
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