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