Chapter 12 ClientServer Systems

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Chapter 12Client/Server Systems
Database Systems Design, Implementation, and
Management 4th Edition Peter Rob Carlos Coronel
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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.

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A Basic Client/Server Computing Model
Figure 12.1
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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 Internets 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

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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

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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

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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

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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

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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
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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.

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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

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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

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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.

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How Client And Server Components Interact
Figure 12.3
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An Example Of Client/Server Architecture
Figure 12.4
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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

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Client/Server Architecture

• Client Components
• Powerful hardware
• An operating system capable of multitasking
• A graphical user interface (GUI)
• Communications capability

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Client Components
Figure 12.5
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Client/Server Architecture

• Server Components
• File services
• Print services
• Fax services
• Communications services
• Database services
• Transaction services
• Miscellaneous services

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Server Components
Figure 12.6
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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

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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).

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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
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Transport Process ID
Figure 12.8
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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

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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

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Database Middleware Components
Figure 12.9
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Interaction Between Client/Server Middleware
Components
Figure 12.10
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Middleware Accessing Multiple Database Servers
Figure 12.11
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Client/Server Architecture

• Middleware Classifications
• Messaging-oriented middleware (MOM)
• Remote-procedure-call-based (RPC-based) middle
  ware
• Object-based middleware

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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

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The Quest for Standards

• Competing Standards
• Client operating systems
• Microsoft Windows 96/98/2000 -- De facto standard
• OS/2, Apples 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, QE

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Client/Server Options
Figure 12.13
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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.

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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.

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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

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Application Logic Components
Figure 12.14
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Client/Server Architectural Styles

• Five Functional Logic Components
• Presentation logic
• I/O processing logic
• Application of business logic
• Data management logic
• Data manipulation logic

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Figure 12.15 Application Functional Logic
Components
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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.

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Functional Logic Splitting In Four Client/Server
Architectural Styles
Figure 12.16
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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.

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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

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Client/Server Implementation Issues

• Changes in the DP Environment Brought by
  Client/Server Computing
• HardwareSingle-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

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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

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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

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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

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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