1. Chapter 6: Client/Server and Intranet Computing
Business Data Communications, 6e

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 Terminology
Application Programming Interface (API): A set of function and call programs that allow clients and servers to intercommunicate.
Client: A networked information requester (usually a PC or workstation) that can query a database and/or other information from a server.
Middleware: A set of drivers, APIs, or other software that improves connectivity between a client application and a server.
Relational Database: A database in which information access is limited to the selection of rows that satisfy all search criteria.
Server: A computer, usually a high-powered workstation or a mainframe, that houses information for manipulation by networked clients.
Structured Query Language (SQL): A language developed by IBM and standardized by ANSI for addressing, creating, updating, or querying relational databases.

4. Client-Server Environment

5. 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

6. 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

7. Classes of Client-Server Applications
Host-based processing
Server-based processing
Client-based processing
Cooperative processing
“Thick client” vs “Thin server”

8. 3-Tier Client/Server Architecture

9. 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).

10. Middleware Architecture

11. Logical View of Middleware

12. Basic Message Passing Primitives

13. 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

14. Remote Procedure Call Mechanism

15. 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

16. 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

17. Intranets
Implementation of Internet-based technologies within an organization, rather than for global connectivity
Immensely successful in corporate computing contexts

18. 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

19. The Intranet Web Web Content Web/Database Connectivity Electronic Mail
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

20. Corporate Intranet Example

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

22. Intranet Webs vs Traditional Client/Server
Client/Server Disadvantages Include: 1. Long development cycles 2. Difficulty in partitioning applications, and modifying based on user feedback 3. Effort in distributing upgrades to clients 4. Difficult in scaling servers to respond to increased load 5. Continuous requirement for more powerful desktop machines

23. 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

24. Extranets
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

25. Advantages of Extranets
Reduced costs
Coordination
Customer Satisfaction
Expedited communication

26. 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

27. Service Oriented Architecture
Client/server architecture utilized widely by enterprise systems
Business functions consist of modular structures

28. SOA Architectural Elements
Service provider: network node that provides a service interface for a software asset that manages a specific set of tasks.
Service requestor: network node that discovers and invokes other software services.
Service broker: specific kind of service provider that acts as a registry and allows lookup of service provider interfaces and service locations.

29. Key Characterisitics for Effective Services Use
Coarse-grained
Interface-based design
Discoverable
Single Instance
Loosely Coupled
Asynchronous

30. SOA Example