Lecture On Introduction (DBMS) By- Jesmin Akhter Assistant Professor, IIT, Jahangirnagar University.

Lecture On

Introduction (DBMS)

By-

Jesmin Akhter

Assistant Professor, IIT, Jahangirnagar University

Database Approach

• Shared collection of logically related data (and a description of this data), designed to meet the information needs of an organization.

• The description of data is known as System Catalog, or Data Dictionary, or Meta Data.

• Is a Single, large repository of data which can be used simultaneously by many users.

• Provides advantages over file system management approach

– Eliminates inconsistency, data anomalies, data dependency, and structural dependency problems

– Stores data structures, relationships, and access paths

PayrollSystem

TaxData

ProjectManagement

System

PersonnelData

ProjectsData

2Prepared by Jesmin Akhter, Assistant Professor , IIT,JU

Prepared by Jesmin Akhter, Assistant Professor , IIT,JU

Main Characteristics of the Database Approach

Self-describing nature of a database system: A DBMS catalog stores the description of the database. The description is called meta-data. This allows the DBMS software to work with different databases. Insulation between programs and data: Called program-data independence. Allows changing data storage structures and operations without having to change the DBMS access programs. Data Abstraction: A data model is used to hide storage details and present the users with a conceptual view of the database. Support of multiple views of the data: Each user may see a different view of the database, which describes only the data of interest to that user. Sharing of data and multiuser transaction processing : allowing a set of concurrent users to retrieve and to update the database. Concurrency control within the DBMS guarantees that each transaction is correctly executed or completely aborted. OLTP (Online Transaction Processing) is a major part of database applications.

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Advantages of Using the Database Approach

Controlling redundancy in data storage and in development and maintenance efforts.Sharing of data among multiple users.Restricting unauthorized access to data.Providing persistent storage for programProviding Storage Structures for efficient Query ProcessingProviding backup and recovery services.Providing multiple interfaces to different classes of users.Representing complex relationships among data.Enforcing integrity constraints on the database.Drawing Inferences and Actions using rules.

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Database Management

• Database is shared, integrated computer structure housing:– End user data– Metadata

• Database Management System (DBMS)– Manages Database structure– Controls access to data– Contains query language

• Definition: A Database Management System (DBMS) is a software that enables users to define, create, and maintain the database.


Importance of DBMS

• Makes data management more efficient and effective

• Query language allows quick answers to ad hoc queries

• Provides better access to more and better-managed data

• Promotes integrated view of organization’s operations

• Reduces the probability of inconsistent data


DBMS Manages Interaction

Figure 1.2


DBMS Functions

• Data dictionary management• Data storage management• Data transformation and presentation• Security management• Multiuser access control• Backup and recovery management• Data integrity management• Database language and application

programming interfaces • Database communication interfaces


ANSI-SPARC Three-Level Architecture

External Level– The users view of the

database.Conceptual Level

– The community view of the database

Internal Level– Physical representation of

the database on the computer.

– Describes how the data is stored in the database.


External level (View)

– A view mechanism:• Provides users with only the data they want or need

to use.

• Reduce complexity;

• Provide a level of security;

• Provide a mechanism to customize the appearance of the database;

• Present a consistent, unchanging picture of the structure of the database, even if the underlying database is changed.


ANSI-SPARC Three-Level Architecture


ANSI-SPARC Objectives:

• Two Types of Data Independence:– Logical Data Independence

• Refers to immunity of external schemas to changes in conceptual schema.

• Conceptual schema changes (add/remove), should not require changes to external schema or rewrites of application programs.

– Physical Data Independence• Refers to immunity of conceptual schema to changes in the

internal schema.• Internal schema changes (e.g. using different file

organizations, storage structures/devices), should not require change to conceptual or external schemas.



Data Independence

• Logical Data Independence: The capacity to change the conceptual schema without having to change the external schemas and their application programs.

• Physical Data Independence: The capacity to change the internal schema without having to change the conceptual schema.

• When a schema at a lower level is changed, only the mappings between this schema and higher-level schemas need to be changed in a DBMS that fully supports data independence. The higher-level schemas themselves are unchanged. Hence, the application programs need not be changed since they refer to the external schemas.

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Multi User DBMS Architectures

• File-server– File-server is connected to several workstations across a

network.• Client-server

– Server holds the database and the DBMS.


File-Server

• Database resides on file-server.

• DBMS and applications run on each workstation.

• Disadvantages include:– Significant network traffic.– Copy of DBMS on each

workstation.– Concurrency, recovery and integrity

control more complex.


Client-Server Architecture

• Client manages user interface and runs applications.

• Advantages include:– wider access to existing

databases;– increased performance;– possible reduction in

hardware costs;– reduction in

communication costs;– increased consistency.


Transaction Processing Monitor as middle tier of a three-tier client-server architecture

• Program that controls data transfer between clients and servers in order to provide a consistent environment, particularly for Online Transaction Processing (OLTP).


Lecture On Introduction (DBMS) By- Jesmin Akhter Assistant Professor, IIT, Jahangirnagar University.

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