Chapter 10: Concepts of DBMS

Chapter 10: Concepts of DBMS

It is a valuable tool for manipulating computerized information for an enterprise or a company or a firm. Manipulation/processing includes, storing, retrieving and modifying the data in a simple manner. So a DBMS consists of a collection of interrelated data and set of programs to access those data.

Comparison of DBMS & Conventional System

DBMS                                      Conventional System

ü Electronic process.              Manual process.

ü No data repeat.                            Repeat the data entry makes wastage of storage.

ü Consistent.                                      Inconsistent data (Repetitions).

ü Errorless.                                 Erroneous information.

ü No missing.                            Missing of data may be occurs.

ü Same format outputs.                  Outputs are in different formats.

ü Easy to allocate data.                 Allocation is too difficult.

ü Speedy process.                            Slow Process.

Advantages of DBMS

•         Reduce Data Redundancy (Duplication of Data).

•         Avoid Inconsistency (Repetition of data).

•         Data can share.

•         Standards can be enforced.

•         Security restrictions can be applied.

•         Integrity can be maintained.

Structure of Database

A database consists of a collection of data is used by application programs of an enterprise. It organized as follows.

w  Fields: Smallest unit of stored data. Each field have different type of data.(Roll no., Name, Score etc..)

w  Record: Collection of related fields. i.e. A group of fields representing a particular information.(Details of one student)

w  File: Collection of all occurrence of one type of records.(Details of students in a class)

Fields, Records and Files in a Database at glance

Components of DBMS

Ø Databases: Organized collection & structure of information.

Ø Data Definition Language (DDL): Database schema specified by a set of definitions is called DDL. It is used to create, Modify and delete the structure of DBMS. It makes a Data Dictionary file after compilation with a set of tables.

§  Also contain data about data called metadata for consultation for manipulation. (Data that describe the properties or characteristics of other data, Metadata allow database designers and users to understand what data exist, what the data mean.)

Ø Data Manipulation Language (DML): Enables to access or manipulate (Insert, edit, update, delete, display) data in DBMS. Provide interface with programming language.

Ø Users: They can interact the DBMS through programs or query languages for manipulations.

Database Design

          Designing a database is done the following three general levels.

Physical Level: It concerned with the storage media.

Logical level: It deals with the relationship of data in a database.

View level: It concerned with the users of databse.

Database Abstraction

          Hiding the unwanted data in a database is called data abstraction. It is restrict the misuse of data.

Levels of database abstraction

§  Physical Level: Here data are stored in primary or secondary storages as bytes. Database hides the bytes.

§  Logical Level: Hide the logical structure and relationship of data. It only used by database administrator.

§  View Level: Hide the details according to the users. It is user level. Only provide the data to the concerned users.

Data independence

                   It means the ability to modify a scheme definition at one level (Physical, Logical, View levels) without affecting the scheme definition at the next higher level is called data independence.

Types of data independence

§  Physical data independence: Modifying the physical schema without causing application programs for improving performance.

§  Logical data independence: Modifying the logical schema without causing application programs. In these two do not effects the other levels of database.

Users of database

§  Database administrator (DBA): A person has central control in data in a DBMS. He is the in charge of creating, modifying and maintaining 3 levels of DBMS. He ensures the consistency and redundancy of data.

§  Application Programmer: They are computer professionals and interacts the DBMS through application programs through DML calls. They give the view level for DBMS.

§  Naive Users/ End users: They are unsophisticated users and they invoking the data through application programs.  So they don't know about the physical and logical structures.

Data Models

                   Design and implementation of any DBMS is done based upon data models. It provides a collection of tool for describing data, data relationship and solves consistency problems. They are: - Hierarchical model, network model and relational model.

Hierarchical model

                   Here lower level record is called child and higher level record is called parent. If the parent record is at the top of the database so it is called root record. Add and deletion must affect the child. It is done through the parent record.

Dis. adv:-

Repeat records, Updating saves separately, Storage become complex.

ex

Network Model

                   Here each child record has more than one parent record. It eliminates redundancy in hierarchical model. It is flexible, can establish different relationships between data. But here the relation is complex, can’t to trace the errors. Data storage is complex

Relational Model

      They are composed of one or more tables made up of rows and columns. Here tables are called relations, rows are called tuples and columns are called attributes. It is flexible, easy to update, doesn't modify all the structure.