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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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Prepared by Jesmin Akhter, Assistant Professor , IIT,JU
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.
Prepared by Jesmin Akhter, Assistant Professor , IIT,JU
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
6Prepared by Jesmin Akhter, Assistant Professor , IIT,JU
DBMS Manages Interaction
Figure 1.2
7Prepared by Jesmin Akhter, Assistant Professor , IIT,JU
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
8Prepared by Jesmin Akhter, Assistant Professor , IIT,JU
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.
Prepared by Jesmin Akhter, Assistant Professor , IIT,JU
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.
Prepared by Jesmin Akhter, Assistant Professor , IIT,JU
ANSI-SPARC Three-Level Architecture
Prepared by Jesmin Akhter, Assistant Professor , IIT,JU
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.
Prepared by Jesmin Akhter, Assistant Professor , IIT,JU
Prepared by Jesmin Akhter, Assistant Professor , IIT,JU
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.
Prepared by Jesmin Akhter, Assistant Professor , IIT,JU
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.
Prepared by Jesmin Akhter, Assistant Professor , IIT,JU
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.
Prepared by Jesmin Akhter, Assistant Professor , IIT,JU
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).
Prepared by Jesmin Akhter, Assistant Professor , IIT,JU