1. 12 Chapter 12 Client/Server Systems Hachim Haddouti

2. 12 2 Hachim Haddouti and Rob & Coronel, Ch12 In this chapter, you will learn: What client/server computing is What the advantages of using client/server systems are client/server architecture, system components and how they interact What effect the client/server system has on the DBMS

3. 12 3 Hachim Haddouti and Rob & Coronel, Ch12 Client/Server Computing Computing model for the development of computerized systems –Client requests specific service –Server provides requested service Reside on same or different computers Figure 12.1

4. 12 4 Hachim Haddouti and Rob & Coronel, Ch12 Client/Server Computing (con’t.) Key to client server power is where request processing takes place Extent of sharing processing –Thin client –Thin server –Fat client –Fat server Classification –2-tier –3-tier

5. 12 5 Hachim Haddouti and Rob & Coronel, Ch12 Forces that Drive Client/Server Trend Changing business environment Growing need for enterprise data access Demand for end-user productivity gains based on efficient use of data Technological advances Growing cost/performance advantages

6. 12 6 Hachim Haddouti and Rob & Coronel, Ch12 Evolution of Computing Environment

7. 12 7 Hachim Haddouti and Rob & Coronel, Ch12 Mainframe vs. Client/Server Systems

8. 12 8 Hachim Haddouti and Rob & Coronel, Ch12 Components of Data-Intensive Systems Three separate types of functionality: Data management Application logic Presentation The system architecture determines whether these three components reside on a single system (“tier) or are distributed across several tiers

9. 12 9 Hachim Haddouti and Rob & Coronel, Ch12 Single-Tier Architectures All functionality combined into a single tier, usually on a mainframe –User access through dumb terminals Advantages: –Easy maintenance and administration Disadvantages: –Today, users expect graphical user interfaces. –Centralized computation of all of them is too much for a central system

10. 12 10 Hachim Haddouti and Rob & Coronel, Ch12 Client-Server Architectures Work division: Thin client –Client implements only the graphical user interface –Server implements business logic and data management Work division: Thick client –Client implements both the graphical user interface and the business logic –Server implements data management

11. 12 11 Hachim Haddouti and Rob & Coronel, Ch12 Two-Tier Client/Server Architecture

12. 12 Hachim Haddouti and Rob & Coronel, Ch12 Client –Front-end application Server –Back-end application Communications middleware –Communications layer Components of Client/Server Architecture

13. 12 13 Hachim Haddouti and Rob & Coronel, Ch12 Client-Server Architectures (Contd.) Disadvantages of thick clients –No central place to update the business logic –Security issues: Server needs to trust clients Access control and authentication needs to be managed at the server Clients need to leave server database in consistent state One possibility: Encapsulate all database access into stored procedures –Does not scale to more than several 100s of clients Large data transfer between server and client More than one server creates a problem: x clients, y servers: x*y connections

14. 12 14 Hachim Haddouti and Rob & Coronel, Ch12 The Three Layers Presentation tier –Primary interface to the user –Needs to adapt to different display devices (PC, PDA, cell phone, voice access?) Middle tier –Implements business logic (implements complex actions, maintains state between different steps of a workflow) –Accesses different data management systems Data management tier –One or more standard database management systems

15. 12 15 Hachim Haddouti and Rob & Coronel, Ch12 The Three-Tier Architecture Database System Application Server Client Program (Web Browser) Presentation tier Middle tier Data management tier

16. 12 16 Hachim Haddouti and Rob & Coronel, Ch12 Three-Tier Client/Server Architecture

17. 12 17 Hachim Haddouti and Rob & Coronel, Ch12 Advantages of the Three-Tier Architecture Heterogeneous systems –Tiers can be independently maintained, modified, and replaced Thin clients –Only presentation layer at clients (web browsers) Integrated data access –Several database systems can be handled transparently at the middle tier –Central management of connections Scalability –Replication at middle tier permits scalability of business logic Software development –Code for business logic is centralized –Interaction between tiers through well-defined APIs: Can reuse standard components at each tier

18. 12 18 Hachim Haddouti and Rob & Coronel, Ch12 Example 1: Airline reservations Build a system for making airline reservations What is done in the different tiers? Database System –Airline info, available seats, customer info, etc. Application Server –Logic to make reservations, cancel reservations, add new airlines, etc. Client Program –Log in different users, display forms and human- readable output

19. 12 19 Hachim Haddouti and Rob & Coronel, Ch12 Example 2: Course Enrollment Build a system using which students can enroll in courses Database System –Student info, course info, instructor info, course availability, pre-requisites, etc. Application Server –Logic to add a course, drop a course, create a new course, etc. Client Program –Log in different users (students, staff, faculty), display forms and human-readable output

20. 12 20 Hachim Haddouti and Rob & Coronel, Ch12 Technologies Database System (SQL Server, Oracle, DB2) Application Server (Tomcat, Apache, IIS) Client Program (Web Browser) HTML Javascript XSLT ASP, JSP Servlets Cookies CGI XML Stored Procedures

21. 12 21 Hachim Haddouti and Rob & Coronel, Ch12 Fast CPU Fault-tolerant capabilities –Dual power –Standby power –Error checking and correcting memory –RAID Expandability of CPU, memory, disk, and peripherals Bus support for multiple add-on boards Multiple communications options Typical Characteristics of Server Hardware

22. 12 22 Hachim Haddouti and Rob & Coronel, Ch12 Client operating systems –Microsoft Windows –OS/2, Apple Mac OS, Unix, Linux Client graphical user interfaces –Microsoft Windows –OS/2 Presentation Manager, Macintosh, UNIX Server operating systems and network protocols –Database servers: Unix, OS/2, Windows NT Server/2000 Server –Printer and file servers: Novell Netware –LAN protocols: TCP/IP, IPX/SPX, NetBIOS Middleware –ODBC, IDAPI, DRDA, Q+E Competing Standards

23. 12 23 Hachim Haddouti and Rob & Coronel, Ch12 Transparent data access to multiple, heterogeneous clients Allow client requests to the database server over network Process client data requests at local server Send only SQL results to clients over network Client/Server DBMS Functions

24. 12 24 Hachim Haddouti and Rob & Coronel, Ch12 Summary: Advantages of Client/Server Systems +Lower network traffic +Improved processing distribution +Thinner clients +Greater processing transparency +Increased network, hardware, and software transparency +Improved security +Decreased costs +Increased scalability

25. 12 25 Hachim Haddouti and Rob & Coronel, Ch12 Management Issues –Communications infrastructure –Applications –Controlling escalating and hidden costs –People and cultural changes –Multiple vendor relationships Development tool acquisition Determination if client/server approach is correct Client/Server Implementation Issues