12 Chapter 12 Client/Server Systems Database Systems: Design, Implementation, and Management 4 th Edition Peter Rob & Carlos Coronel
What Is Client/Server Computing? 12 4 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. 4 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. u The client/server environment provides a clear separation of server and client processes. u
A Basic Client/Server Computing Model 12 Figure 12. 1
The Forces That Drive C/S Systems 4 The Changing Business Environment Global market dynamics and competitive pressure u Need for fast, efficient, and widespread data access u 12 4 The Need for Enterprise Data Access 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 u 4 End 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
The Forces That Drive C/S Systems 4 Technological Advances u 12 u u Microprocessor Technology Data Communication and the Internet Database Systems Operating Systems and Graphical User Interfaces (GUIs) Sophisticated PC-Based End User Application Software 4 Cost/Performance Advantages of the PC-Based Platform 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 u
The Evolution of Client/Server IS 4 Mainframes in the 1970 s 12 u u u Complex, proprietary OS Dumb terminals Restricted access Hardware and software dictated IS Centralized, complex MIS department bureaucracy 4 Microcomputers in the 1980 s Easy-to-use software (e. g. , spreadsheet) u Micro-based database systems u Data still in mainframes u “Manual download” u
The Evolution of Client/Server IS 4 Intelligent Terminals 12 u u u PCs connected to the mainframe Electronic download Proliferation of snapshot versions of corporate DB Islands of information Sneaker net 4 Local Area Network operating systems (NOS) u Powerful PCs u Common platform for both end users and MIS specialists u
The Evolution of Client/Server IS 4 Computer Landscape of the 1990 s 12 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
12 Figure 12. 2 The Evolution Of The Computing Environment
12 Table 12. 1 Contrasting Mainframe and Client/Server Information Systems
Managerial Expectations of C/S Systems 4 Client/Server Benefits 12 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 u 4 Observations 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. u
Managerial Expectations of C/S Systems 4 MIS Expectations of Client/Server Benefits 12 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 4 Organizational Expectations of Client/Server Benefits 12 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
Client/Server Architecture 4 Three Components of Client/Server Architecture 12 u The client is any computer process that requests services from the server. It is also known as the frontend 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.
How Client And Server Components Interact 12 Figure 12. 3
An Example Of Client/Server Architecture 12 Figure 12. 4
Client/Server Architecture 4 Client/Server Principles u 12 Hardware independence u Software independence l l l Operating systems Network systems Applications u Open access to services u Process distribution l l u Process autonomy Maximization of local resources Scalability and flexibility Interoperability and integration Standards
Client/Server Architecture 4 Client Components 12 u Powerful hardware u An operating system capable of multitasking u A graphical user interface (GUI) u Communications capability
Client Components 12 Figure 12. 5
Client/Server Architecture 4 Server Components 12 u File services u Print services u Fax services u Communications services u Database services u Transaction services u Miscellaneous services
Server Components 12 Figure 12. 6
Client/Server Architecture 4 Characteristics of Server Hardware u 12 u u Fast CPU Fault-tolerant capabilities Expandability of CPU, memory, disk, and peripherals Bus support for multiple add-on boards Multiple communications options 4 Server Process Benefits from the Client/Server Architectural Principles Location independence u Resource optimization u Scalability u Interoperability and integration u
Client/Server Architecture 4 Communications Middleware Components 12 u The use of database middleware yields l l u Network independence Database server independence 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).
12 Table 12. 2 The OSI Network Reference Model
12 Figure 12. 7 Information Flow Through The OSI Model
Transport Process ID 12 Figure 12. 8
Client/Server Architecture 4 Network Protocols u 12 Transmission Control Protocol/Internet Protocol (TCP/IP) l u Internetwork Packet Exchange/ Sequenced Packet Exchange (IPX/SPX) l l u 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 (Net. BIOS) l l u 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) l Used in IBM mainframe Systems Network Architecture (SNA) environments
Client/Server Architecture 4 Database Middleware Components 12 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. 4 Three Main Benefits of Using Middleware u Access multiple databases u Database server-independent u Network protocol-independent
Database Middleware Components 12 Figure 12. 9
Interaction Between Client/Server Middleware Components 12 Figure 12. 10
Middleware Accessing Multiple Database Servers 12 Figure 12. 11
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Client/Server Architecture 4 Middleware Classifications 12 u Messaging-oriented middleware (MOM) u Remote-procedure-call-based (RPC-based) middle ware u Object-based middleware
The Quest for Standards 4 Standard-Setting Organizations 12 u IEEE (Institute of Electrical and Electronics Engineers) l u ANSI (American National Standards Institute) l u Network and hardware Programming languages (e. g. , COBOL, SQL) ISO (International Standards Organization) l OSI (Open Systems Interconnection) reference
The Quest for Standards 4 Competing Standards u 12 Client operating systems l l u Client graphical user interfaces l l u Microsoft Windows 96/98/2000 -- De facto standard OS/2 Presentation Manager, Macintosh, UNIX (e. g. , Notif, Open. Look) Server operating systems and network protocols l l l u 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, Net. BIOS Middleware l ODBC, IDAPI, DRDA, Q+E
Client/Server Options 12 Figure 12. 13
Client/Server Databases 4 Functions of the Client/Server Database 12 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.
Client/Server Databases 12 4 Characteristics 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.
Client/Server Architectural Styles 4 Two Key Questions for the Client/Server Architecture How is the division made? u Where in the system should the results of that division be placed? u 12 4 Three Application Logic Components Input/Output (I/O) u Processing u l l l u I/O processing logic Application or business logic Data management logic Storage
Application Logic Components 12 Figure 12. 14
Client/Server Architectural Styles 4 Five Functional Logic Components 12 u Presentation logic u I/O processing logic u Application of business logic u Data management logic u Data manipulation logic
12 Figure 12. 15 Application Functional Logic Components
Client/Server Architectural Styles 4 Typical Logic Component Placement 12 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.
Functional Logic Splitting In Four Client/Server Architectural Styles 12 Figure 12. 16
Client/Server Architectural Styles 4 Notes on Figure 12. 16 u 12 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.
Client/Server Implementation Issues 4 Client/Server versus Traditional Data Processing 12 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
Client/Server Implementation Issues 4 Changes in the DP Environment Brought by Client/Server Computing 12 u Hardware Single-vendor-dependent Integration of different hardware platforms u Software Mainframe, 3 GL GUI, networks, communications u Data Centralized, single repository Distributed, multiple formats u Procedures Centralized, rigid, complex Flexible, decentralized u People Requires support and training for new skills and technology
Client/Server Implementation Issues 4 Managerial Considerations 12 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
Client/Server Implementation Issues 4 Client/Server Development Tools 12 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
Client/Server Implementation Issues u 12 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 4 An Integrated Approach 12 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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