The Internal Level Physical Level

Published Date: 02 Nov 2017

Designing a database is much like designing anything like a building, a car, a roadway through a city, or a book etc. Much care must be taken to plan a design. If time is not taken to carefully plan the design of an object, the quality of the end product will suffer. Database design can be debated indefinitely what to include, what not to include, and in what order to present the material. The approach for database design is about database design focuses mainly on the logical methods involved in deriving a database structure. We explain the thought process involved in converting an organization’s data storage needs into a relational database.

Components of DBMS:-

Software

Hardware

Data

Procedures

Data base access Language

SOFTWARE:-

The main component of DBMS is software. It is the set of program used to handle the database and to control and manage the overall computerized database.

DBMS software itself is the most imp. software component in the overall system.

OS including network software being used in network, to share the data of database among multiple users.

Application programs developed in programming languages such as C++, visual basic that are used to access DBMS. Each program contains statements that request the DBMS to perform operating on database. The operating may include retrieving, updating, deleting data etc. the application program may be conventional or online workstation or terminal.

Hardware:-

Hardware consists of a set of physical electronic devices such as computers, storage devices and I/O channels electromechanical devices that make interface b/w compuers and the real world system etc and so on. It is impossible to implement the DBMS without the hardware devices, in a network, a powerful computer with high data processing speed and a storage devices device with large storage capacity is required as database server.

Data:-

Data is the most imp. Component of the DBMS. The main purpose of DBMS is to process the data. In DBMS, database are defined, constructed and then data is stored, updated and retrieved to and from the database.

PROCEDURES- The user may use and manage the DBMS documented procedures on hot use or run the DBMS-

Procedure to install new DBMS

To log on to the DBMS

To use DBMS or application program

To make backup copies of the database

To change the structure of the database

To generate the reports of the data retrieved from database

Database Access Language:-

The database access language is used to access the data to form the database. The users use the database access language to enter new data, change the existing data in database and to retrieve data from database. The users write a set of appropriate commands in a database access language and submit these to the DBMS.

Architecture In DBMS

There are 3 levels of architecture in DBMS which are as follows:-

External Level

Conceptual Level

Internal Level

The External Level / View Level:-

This level has no. of external schema`s. Each external schema describes the part of database that a particular user group is interested about it and it prevents the rest of database from this user group.

Application programmer uses a HOST LANGUAGE: COBOL, PL/1, C

Embedded in the host language is a DATA SUBLANGUAGE DSL example SQL, DBASE

Data sublanguage consists of Data Definition Language DDL, Data Manipulation Language DML

Data Definition Language declares objects

Data Manipulation Language manipulates database objects e.g. retrievals and updates

The Conceptual Level:-

This level has a conceptual schema which describes the structure of the whole database for a community of users. This schema prevents the details of the physical storage and concentrates on the description of entities data types, relation and users operation. In other ways a representation model is used to describe the conceptual schema, when a database system is implemented.

A representation of the entire information content of the database

The conceptual schema is a definition of the view of the total database content

Conceptual schema, in most cases, is the union of external schemas

One can add security and integrity checks, semantic models and data dictionary

The Internal Level / Physical Level:-

This Level has an internal schema which describes the physical storage of the database. The internal schema uses a physical model and describes the complete details of data storage and also describes the execution path for the database.

The internal view is a low-level representation of the entire database

Internal record, or stored, is built upon physical record, or pages and blocks.

The Three Schema Architecture is a convenient tool with which the user can visualize the schema level in a database system. Most of the DBMS do not separate this three level completely.