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Chapter 7: Client/Server Computing

Chapter 7: Client/Server Computing. Business Data Communications, 5e. 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

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Chapter 7: Client/Server Computing

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  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. 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 Message Passing Issues

  13. Remote Procedure Call Mechanism

  14. 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 Client/Server Binding

  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. 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 Advantages of Intranets

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

  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 company’s intranet data • Internet access to an external server that originates database queries to internal servers • Virtual private network

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