Database Management Systems 2

1. Database Management Systems 2 ANGELITO I. CUNANAN JR.

2. I. Database Management Systems Approaches… • Client/Server Systems • Advantages • Disadvantages • Distributed Database • Characteristics of DBMSs • Advantages • Disadvantages • Rules for distributed database • Centralized Database • Advantages • Disadvantages • Federated Database • FDBS Architecture • 5 Level Schema

3. Client/Server Systems… File Server stores the files required by the users on the network. When users need data from file or a group of files, they send requests to the file server. The file server then sends the requested file or files to the user’s computer; that is, the file server sends entire files, not just the data need by users.

4. Client/Server Systems…(continued) USER B User requests file(s) from the file server USER A USER C NETWORK File server sends requested file(s) to the user FILE SERVER FILES ON DISK File server architecture

5. Client/Server Systems…(continued) In Client/Server terminology, the Server is a computer providing data to the clients, which are the computers that are connected to a network and that people use to access data stored on the server. • Server is also called a back-end processor or back-end machine. • Client is also called a front-end processor or front-end machine.

6. Guide… • In client/server architecture, DBMS runs on the server. • Client sends a request to the server, notentire files but for specific data. • Compared to a file server architecture, a client/server architecture reduces communication activity on a network, which reduces delays in supplying data to users. • Clients & Server: Performs different functions, can run in different OS, this arrangement of client/server architecture is called two-tier architecture. • Server – performs database function, client – performs presentation function (user interface function).

7. Guide…(continued) • Business function – Calculations, commissions, taxes, and order totals. • Fat client – Client perform business functions. (Client maintenance problem). • Thinclient – Server performs business functions. (Scalability problem). • Scalability – Is the ability of a computer system to continue to function well as utilization of the system increases. • Three-tier architecture – Client perform presentation functions, Database Server performs database function, and separate computer (called Application servers) perform business functions and serves as interface between client and database server. (also referred to n-tier architecture).

8. Client/Server Systems…(continued) Fat Client Thin Client Scalability Three-tier architecture

9. Client/Server Systems…(continued) USER B User requests data from database USER A USER C NETWORK Servers ends only requested data to the client that requested it SERVER WITH A DBMS DATABASE Two-tier client/server architecture

10. Client/Server Systems…(continued) Clients perform presentation functions USER B USER A USER C NETWORK Database server runs the DBMS and performs database functions Application server performs business functions APPLI-CATION SERVER DATA-BASE SERVER DATABASE Three-tier client/server architecture

11. Advantages of Client/Server Systems… • Lower Network Traffic. A client/server system transmits only the necessary data, rather than entire files, across the network. • ImprovedProcessingDistribution. Let you distribute processing functions among multiple computers. • ThinnerClients. Because the application and database server handle most of the processing in a client/server system, clients do not need to be as powerful or as expensive as the would in a file-server environment. • GreaterProcessingTransparency. As far as a user is concerned, all processing occurs on the client just as it does on a stand-alone system. Users do not need to learn any special commands or techniques to work in a client/server environment.

12. Advantages of Client/Server Systems…(continued) • Increased Network, Hardware, and Software Transparency. A single operation could access data from different networks, different computers, and different OS. • Improved Security. In addition to security features of DBMS on database server, you can place additional security features on the application servers and on the network. • Decreased Cost. Client/server systems have proven to be powerful enough that organizations have replaced, at a considerable cost savings, enterprise applications and mainframe databases with PC applications and database managed by client/server systems. • Increased Scalability. If an application server or database server becomes a bottleneck, you can upgrade the appropriate server or add additional processors to share the processing load.

13. Distributed Database Is a single logical database that is physically divided among computers at several sites on a network.

14. Property of Distributed DBMSs (DDBMS)… • Homogeneous DDBMS is one that has the same local DBMS at each site. • Heterogeneous DDBMS is one that does not; there are at least two sites at which the local DBMSs are different.

15. Characteristics of Distributed DBMSs (DDBMS)… • Location Transparency • Replication Transparency • Fragmentation Transparency

16. Advantages of Distributed Database… • Local control of data • Increasing database capacity • System availability • Improved performance

17. Disadvantages of Distributed Database…(continued) • Update of replicated data • More complex query processing • More complex treatment of concurrent update • More complex recovery measures • More difficult management of the data dictionary

18. Advantages of Distributed Database…(continued) • More complex database design • More complicated security and backup requirements

19. Rules for Distributed Databases • Local autonomy • No reliance on a central site • Continuous operation • Location transparency • Fragmentation transparency • Replication transparency • Distributed query processing • Distributed transaction management • Hardware independence • Operating system independence • Network Independence • DBMS independence