Categories

A sample text widget

Etiam pulvinar consectetur dolor sed malesuada. Ut convallis euismod dolor nec pretium. Nunc ut tristique massa.

Nam sodales mi vitae dolor ullamcorper et vulputate enim accumsan. Morbi orci magna, tincidunt vitae molestie nec, molestie at mi. Nulla nulla lorem, suscipit in posuere in, interdum non magna.

DBMS Three-Schema Architecture and Data Independence

WHAT IS DBMS ?
– To be able to carry out operations like insertion, deletion and retrieval, the database needs to be managed by a substantial piece of software; this software is usually called a Database Management System(DBMS).
– A DBMS is usually a very large software package that enables many different tasks including the provision of facilities to enable the user to access and modify information in the database.
– Data Description Languages (DDL) and Data Manipulation Languages (DML) are needed for manipulating and retrieving data stored in the DBMS. These languages are called respectively.

An architecture for database systems, called the three-schema architecture was proposed to help achieve and visualize the important characteristics of the database approach.

THE THREE-SCHEMA ARCHITECTURE:
The goal of the three-schema architecture is to separate the user applications and the physical database. In this architecture, schemas can be defined at 3 levels :
1. Internal level or Internal schema : Describes the physical storage structure of the database. The internal schema uses a physical data model and describes the complete details of data storage and access paths for the database.
2. Conceptual level or Conceptual schema : Describes the structure of the whole database for a community of users. It hides the details of physical storage structures and concentrates on describing entities, data types, relationships, user operations, and constraints. Implementation data model can be used at this level.
3. External level or External schema : It includes a number of external schemas or user views. Each external schema describes the part of the database that a particular user is interested in and hides the rest of the database from user. Implementation data model can be used at this level.

DBMS Three-Schema architecture

IMPORTANT TO REMEMBER :
Data and meta-data
– three schemas are only meta-data(descriptions of data).
– data actually exists only at the physical level.
Mapping
– DBMS must transform a request specified on an external schema into a request against the conceptual schema, and then into the internal schema.
– requires information in meta-data on how to accomplish the mapping among various levels.
– overhead(time-consuming) leading to inefficiencies.
– few DBMSs have implemented the full three-schema architecture.

DATA INDEPENDENCE

The disjointing of data descriptions from the application programs (or user-interfaces) that uses the data is called data independence. Data independence is one of the main advantages of DBMS. The three-schema architecture provides the concept of data independence, which means that upper-levels are unaffected by changes to lower-levels. The three schemas architecture makes it easier to achieve true data independence. There are two kinds of data independence.

– Physical data independence
* The ability to modify the physical scheme without causing application programs to be rewritten.
* Modifications at this level are usually to improve performance.

– Logical data independence
* The ability to modify the conceptual scheme without causing application programs to be rewritten.
* Usually done when logical structure of database is altered.

Logical data independence is harder to achieve as the application programs are usually heavily dependent on the logical structure of the data. An analogy is made to abstract data types in programming languages.

Database Management Systems Fundamentals of Database Systems First Course in Database Systems

5 comments to DBMS Three-Schema Architecture and Data Independence

  • ravi

    when does logical structure of a database get altered?

  • Perez

    Interested as dbms student

  • MD.ZAHID GANI

    DBMS vs. RDBMS

    • Relationship among tables is maintained in a RDBMS whereas this not the case DBMS as it is used to manage the database.

    • DBMS accepts the ‘flat file’ data that means there is no relation among different data whereas RDBMS does not accepts this type of design.

    • DBMS is used for simpler business applications whereas RDBMS is used for more complex applications.

    • Although the foreign key concept is supported by both DBMS and RDBMS but its only RDBMS that enforces the rules.

    • RDBMS solution is required by large sets of data whereas small sets of data can be managed by DBMS.

    DBMS

    DBMS is defined as the software program that is used to manage all the databases that are stored on the network or system hard disk. There are different types of database management systems and some of them are configured for specific purposes.

    DBMS is available in different forms as a tool that is used to manage databases. Some popular DBMS solutions include DB2, Oracle, FileMaker and Microsoft Access. Using these products, privileges or rights can be created that can be specific to particular users. It means that the administrators of the database can grant specific rights to some users or assign different levels of administration.

    Every DBMS has some fundamental elements. First is the implementation of the modeling language which defines the language used for each database. Second, DBMS also administers the data structures. Data query language is the third element of a DBMS. Data structures work with data query language in order to make sure that irrelevant data cannot be entered into the database used in the system.

    RDBMS

    The database system in which the relationships among different tables are maintained is called Relational Database Management System. Both RDBMS and DBMS are used to store information in physical database.

    RDBMS solution is required when large amounts of data are to be stored as well as maintained. A relational data model consists of indexes, keys, foreign keys, tables and their relationships with other tables. Relational DBMS enforces the rules even though foreign keys are support by both RDBMS and DBMS.

    In 1970s, Edgar Frank Codd introduced the theory of relational database. Thirteen rules were defined by Codd for this relational theory or model. Relationships among different types of data Is the main requirement of the relational model.

    RDMS can be termed as the next generation of database management system. DBMS is used as a base model in order to store data in a relational database system. However, complex business applications use RDBMS rather than DBMS.

    Read more: http://www.differencebetween.com/difference-between-dbms-and-rdbms/#ixzz1PDw9F4by

  • karthi

    why we have this( 3 schema architecture in dbms )? why we did use 2 r 4 schema architecture?

  • Eng.maram/USA

    very very very coooool explanation to fresher engineer in DBMS….thank thxxxxxx 😀

Leave a Reply

You can use these HTML tags

<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>