DATABASE MANAGEMENT

SYSTEMS 2ANGELITO I. CUNANAN JR.

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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

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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.

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Client/Server Systems…(continued)

USER A

USER B

USER C

NETWORK

FILE SERVE

RFILES ON DISK

User requests

file(s) from the file server

File server sends

requested file(s) to the

user

File server architecture

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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.

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Guide…

•In client/server architecture, DBMS runs on the server.

•Client sends a request to the server, not entire 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).

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Guide…(continued)

•Business function – Calculations, commissions, taxes, and order totals.

•Fat client – Client perform business functions. (Client maintenance problem).

•Thin client – 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).

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Client/Server Systems…(continued)Fat Client

Thin Client

Scalability

Three-tier architecture

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Client/Server Systems…(continued)

USER A

USER B

USER C

NETWORK

SERVER

WITH A

DBMS

DATABASE

User requests data from database

Servers ends only

requested data to the client that

requested it

Two-tier client/server architecture

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Client/Server Systems…(continued)

USER A

USER B

USER C

NETWORK

DATA-BASE SERVE

R

DATABASE

Database server runs the DBMS

and performs database functions

Application server

performs business functions

Three-tier client/server architecture

APPLI-CATIO

N SERVE

R

Clients perform

presentation functions

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Advantages of Client/Server Systems…•Lower Network Traffic. A client/server system transmits only the necessary data, rather than entire files, across the network.

•Improved Processing Distribution. Let you distribute processing functions among multiple computers.

•Thinner Clients. 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.

•Greater Processing Transparency. 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.

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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.

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Distributed Database

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

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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.

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Characteristics of Distributed DBMSs (DDBMS)…•Location Transparency

•Replication Transparency

•Fragmentation Transparency

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Advantages of Distributed Database…•Local control of data

•Increasing database capacity

•System availability

•Improved performance

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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

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Advantages of Distributed Database…(continued)•More complex database design

•More complicated security and backup requirements

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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