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