Database Management System

Contents Definition Components Advantages Limitations

Contents

DBMS Functions Architecture

ement

DBMSA set of programs used to access, update & manage the data is called Database Management System. e.g. dBase, Foxpro, Oracle etc.

Key characteristics of DBMS are: performance, store large volume of database, share data, provide security, remove redundancy and provide concurrent access.

Functions of DBMS Creating a Database :

DBMS provides different commands to perform operations on database system. Database system can be created through DBMS commands. e.g. Create command is used to create database file in dBase, Foxpro, Oracle. This command declares structure of database system.

Functions Contd.. Data Manipulation :

DBMS provides no. of commands to manipulate data stored in database system. These commands can be related to arithmetic operations or for sorting & searching of data files etc.

Data Retrieval : No. of commands are available in DBMS to provide required data to users.

Functions Contd.. Data Security & Integrity :

DBMS must monitor user request & reject any attempt violate security & integrity rules defined by DBA.

Data Recovery & Concurrency : DBMS must enforce certain recovery & concurrency control.

Functions Contd.. Data Dictionary :

DBMS must provide data dictionary function. Data Dictionary contains information about entities, attributes, mapping & cross reference information.

Architecture of DBMS

Architecture of DBMS is divided into three levels that can be expressed as :

1. Internal Level2. Conceptual Level3. External Level

Architecture Contd..

External / Conceptual Mapping

Internal / Conceptual Mapping

Architecture Contd..

1. Internal Level : This level is closest to physical level & it represents

how data is represented in storage device. There can be more than one data files at internal level. The records at internal level are represented by internal schema.

2. Conceptual Level :It is one which represents database in its totality. All the different files at internal are combined together logically to create conceptual level.

Architecture Contd..

There will be only one conceptual level in database system. Conceptual level is defined in terms of conceptual schema & records are defined as conceptual records.

3. External Level :Level which is closest to the user is called external level. It represents how the data is seen by individual user. In fact, it is a part of conceptual level data.

Architecture Contd..

There can be more than one external level views. Here, the data can be represented in the form of conceptual schema.

Mappings :Two mappings are required in database system with three different views : Internal / Conceptual MappingExternal / Conceptual Mapping

Architecture Contd..

Internal / Conceptual Mapping :It represents association between data items at conceptual level & data items at internal level. It shows how conceptual level is obtained from internal level. Whenever there is a change in internal level, this mapping also change so that conceptual level remains un-effected. In other words, physical data independence is obtained by this mapping.

Architecture Contd..

External / Conceptual Mapping :Association between external records & conceptual records is called external / conceptual mapping. This defines how external records are obtained from conceptual records. Whenever there is any change in requirement at external level, this mapping also change so that conceptual level remains un-effected. In other words, physical data independence is obtained by this mapping.

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