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Chapter 7: Client/Server Computing

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Title: Business Data Communications 4e Subject: Chapter 17: Client/Server Computing Author: Elizabeth Lane Lawley Last modified by: Elizabeth Lawley – PowerPoint PPT presentation

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Title: Chapter 7: Client/Server Computing


1
Chapter 7 Client/Server Computing
  • Business Data Communications, 5e

2
What is Client/Server?
  • Client
  • Server
  • Network
  • How is client/server different from other
    distributed computing?
  • Heavy reliance on user-friendly applications
  • Emphasis on centralizing databases and management
    functions
  • Commitment to openness/modularity
  • Networking fundamental to operation

3
Client-Server Environment
4
Why is Client-Server Different?
  • Emphasis on user-friendly client applications
  • Focus on access to centralized databases
  • Commitment to open and modular applications
  • Networking is fundamental to the organization

5
Client/Server Applications
  • Emphasis on GUI for users
  • Database Example
  • Database on server, applications for access on
    client, glue (like SQL) enables requests)
  • Application logic can be client-only, or split
    between client and server

6
Classes of Client-Server Applications
  • Host-based processing
  • Server-based processing
  • Client-based processing
  • Cooperative processing
  • Fat client vs fat server

7
3-Tier Client/Server Architecture
8
Middleware
  • Standardized interfaces and protocols between
    clients and back-end databases
  • Hides complexity of data sources from the
    end-user
  • Compatible with a range of client and server
    options
  • All applications operate over a uniform
    applications programming interface (API).

9
Middleware Architecture
10
Logical View of Middleware
11
Basic Message Passing Primitives
12
Message Passing Issues
  • Reliability vs Unreliability
  • Reliable facilities guarantee delivery, provide
    error-checking, retransmission, etc
  • Alternatively, the message can be sent without
    success/failure reduces complexity and overhead,
    passes responsibility for confirmation to
    application
  • Blocking vs Nonblocking
  • Non-blocking more efficient, but difficult to
    test and debug programs
  • Blocking (synchronous) retains control until
    acknowledgment is received

13
Remote Procedure Call Mechanism
14
Client/Server Binding
  • Nonpersistent binding
  • Does not maintain state information, connections
    re-established as necessary
  • Inappropriate for RPCs used frequently by same
    caller
  • Persistent binding
  • Connection sustained until procedure return
  • Useful for applications making repeated calls to
    remote procedures

15
Object-Oriented Mechanisms
  • Clients and servers ship messages between
    objects.
  • May rely on an underlying message or RPC
    structure or be developed directly on top of
    object-oriented capabilities in the operating
    system
  • Success depends on standardization of the object
    mechanism, but competing models exist
  • COM, OLE, CORBA

16
Intranets
  • Implementation of internet-based client/server
    technology within an organization, rather than
    for global connectivity
  • Immensely successful in corporate computing
    contexts

17
Advantages of Intranets
  • Rapid prototyping
  • Scales effectively
  • Little training required
  • Can be implemented on variety of systems
  • Open architecture allows interaction across
    platforms
  • Supports a range of distributed servers
  • Allows integration of legacy systems on client
    and server side
  • Supports a range of media types
  • Inexpensive to implement

18
The Intranet Web
  • Web Content
  • The web can be used to effectively distribute
    content in a way that requires no new training
    for end-users
  • Web/Database Connectivity
  • Multiple tools exist to serve as middleware
    between web servers and data sources
  • Electronic Mail
  • Network News

19
Web/Database Connectivity
  • Advantages
  • Ease of administration
  • Deployment
  • Development speed
  • Flexible information presentation
  • Disadvantages
  • Limited functionality
  • Stateless operation makes tracking difficult

20
Intranet Disadvantages
  • Long development cycles
  • Difficulty in partitioning applications, and
    modifying based on user feedback
  • Effort in distributing upgrades to clients
  • Difficult in scaling servers to respond to
    increased load
  • Continuous requirement for more powerful desktop
    machines

21
Other Intranet Technologies
  • Electronic Mail
  • Closed internal mail systems (delivery
    verification, etc)
  • Internal mailing lists
  • Network news (USENET)
  • Can be adopted for internal intranet uses

22
The Extranet Web
  • Extends the intranet concept to provide
    information and services to selected outside
    populations, such as customers and suppliers
  • Enables the sharing of information between
    companies
  • A TCP/IP enabled form of EDI

23
Advantages of Extranets
  • Reduced costs
  • More marketable products
  • Increased productivity
  • Enhanced profits
  • Reduced inventories
  • Faster time to market

24
Methods for Converting Intranets to Extranets
  • Long-distance dial-up access
  • Internet access to intranet with security
  • Internet access to an external server that
    duplicates some of a companys intranet data
  • Internet access to an external server that
    originates database queries to internal servers
  • Virtual private network
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