1. Chapter 12 Client/Server Systems
Database Systems: Design, Implementation, and Management
4th Edition
Peter Rob & Carlos Coronel 1

2. 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. 4

3. A Basic Client/Server Computing Model
Figure 12.1 5

4. 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 Internet’s 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 6

5. 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 6

6. 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” 7

7. 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 8

8. 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 8

9. Figure 12.2 The Evolution Of The Computing Environment9

10. Table 12.1 Contrasting Mainframe and Client/Server Information Systems10

11. 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. 11

12. 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 12

13. 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 13

14. 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. 14

15. How Client And Server Components Interact
Figure 12.3 15

16. An Example Of Client/Server Architecture
Figure 12.4 16

17. 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 17

18. Client/Server Architecture
Client Components
Powerful hardware
An operating system capable of multitasking
A graphical user interface (GUI)
Communications capability 18

19. Client Components
Figure 12.5 19

20. Client/Server Architecture
Server Components
File services
Print services
Fax services
Communications services
Database services
Transaction services
Miscellaneous services 20

21. Server Components
Figure 12.6 21

22. 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 22

23. 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). 24

24. Table 12.2 The OSI Network Reference Model25

25. Figure 12.7 Information Flow Through The OSI Model26

26. Transport Process ID
Figure 12.8 27

27. 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 28

28. 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 29

29. Database Middleware Components
Figure 12.9 30

30. Figure 12.10 Interaction Between Client/Server Middleware Components31

31. Middleware Accessing Multiple Database Servers
Figure 12.11 32

32. 33

33. Client/Server Architecture
Middleware Classifications
Messaging-oriented middleware (MOM)
Remote-procedure-call-based (RPC-based) middle ware
Object-based middleware 34

34. 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 35

35. The Quest for Standards
Competing Standards
Client operating systems
Microsoft Windows 96/98/ De facto standard
OS/2, Apple’s Mac OS 8.5, Unix including Linux
Client graphical user interfaces
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, Q+E 36

36. Client/Server Options
Figure 12.13 37

37. 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. 38

38. 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. 39

39. 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 40

40. Application Logic Components
Figure 12.14 43

41. Client/Server Architectural Styles
Five Functional Logic Components
Presentation logic
I/O processing logic
Application of business logic
Data management logic
Data manipulation logic 42

42. Figure 12.15 Application Functional Logic Components43

43. 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. 44

44. Figure 12.16 Functional Logic Splitting In Four Client/Server
Architectural Styles
Figure 12.16 43

45. 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. 46

46. 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 47

47. Client/Server Implementation Issues
Changes in the DP Environment Brought by Client/Server Computing
Hardware Single-vendor-dependent  Integration of different hardware platforms
Software Mainframe, 3GL  GUI, networks, communications
Data Centralized, single repository  Distributed, multiple formats
Procedures Centralized, rigid, complex  Flexible, decentralized
People Requires support and training for new skills and technology 48

48. 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 49

49. 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 50

50. 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 51

51. 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 52