RDBMS

Table of Contents

Data Models: 

A Database Management System is a Software used to store and manage data. A DBMS stores data in database and users data models to show the various ways of managing data.
A Relational Database Management system (RDBMS) is an advanced various of a DBMS that also defines the relationship between the various data values.

In this chapter we introduce DBMS and Describes the various type of data models.

Objectives:
In this chapter,you can learn to:

• Define a database management system.
• Describe the type of data models.
• Define a relational database management system.
• Describe the operational that work on relations.

Database Management System:

A database is a collection of logically related data.data means know facts, which are meaningful and can be recorded. For example, names telephone number. we can record this data in an indexed address book or on a hard disk, by using software such as Microsoft Access or Microsoft Excel.

Database Management is the task of maintaining database so that the information is easily available. The software required to perform the task of database management is called a database management system(DBMS).DBMSs are designed to maintain large volumes of data.

Management of data involves.

• Defining structures for data storage.
•  Providing methods for data manipulation, such as adding, editing, and deleting data.
• Providing data security against unauthorized assess.

The main objectives of any DBMS are to:-

• Provide an efficient and easy way to store, update, and retrieve database.
• Manage information about users who intact with the DBMS, and the tasks that these users can perform on the data.

Data Model:-

A data model is a description of data in a database.In data model describe the relationship among data, and any constraints that have to be defined on the data. The data model can broadly be classified into the following categories:

• Object-base logical model: Focuses on describing the data , the relationship among the data, and any constraints defined.
• Record-base logical model: Focuses on specifying the logical structuring of the database. 

Object-Base logical model:-

There are various object-based logical model:-

• ER Model.
• Object-oriented model
• Binary model

Note:- The most widely used is the ER model. It is accepted as an ideal data model for the database design.

  

ER-Model:- The ER-Model views the real world as a collection of objects or entities and the relationship among them,Chen introduced not only the ER model, but also corresponding diagramming technique.
The following diagram show various components and depicts the relationship between them.

 

In the preceding diagram,COURSE and SEMESTER and two entities.The COURSE entity contains two attributes,TITLE and CODE. The SEMESTER entity contains three attributes: START-DT , END-DT, and SEM#. The COURSE and SEMESTER entities are related through a relationship,TAUGHT.

Chen defined an entity as "a thing,which can be easily identified". An entity is any object, place,person,or activity about which data is recorded. An entity can be categorized as entity type and entity instance.An entity type is a set of things that share common properties. 

Now in this ER Model diagramming technique, entities anr named and represented inside a box. An entity type is usually represented in uppercase in the ER model..We are following diagram consists of three types:-

• STUDENT.
• COURSE.
• GRADE. 

We have represented inside a box.

Entities:
There are two types of entities.

• Dependent.
• Independent.

Dependent Entities:- The dependent entities is a depends on another entity is called a dependent entity.

Independent Entities:- The independent entities is a dose not depend on any other entity for existence.Dependent entities are also called weak entities, and independent entities are called regular entities.

Relationships

We have defined relationship as "an association among entities''. For Example there is a relationship between student and teachers.This relationship represents the fact that a teacher teaches several student and a student is taught by several teachers..This relationship represents the fact that a relationship could be named TEACH.

A relationship is depicted as a diamond with the name of the relationship type. The following diagram consists of two entities, TEACHER and STUDENT,which are associated with a relationship,TEACH.

A relationship can associate an entity with itself. For example,one teacher in a university may marry another teacher.

The following diagram represents the association of an entity with itself.

Relationship

There are three type of relationships

• One-to-One 
• One-to-Many(Or Many-to-One)
• Many-to-Many

One-to-One Relationship:-
Consider an example of a university. For a particular DEPARTMENT,such as electronics,there can be only one DEPARTMENT HEAD. 
This is an example of a one-to-one relationship.The following diagram represent the one-to-one relationship between DEPARTMENT and DEPARTMENT HEAD.

 Many-to-One Relationship:-
A STUDENT can MAJOR in only one course,but many STUDENT's can register for a given MAJOR course. 
This is an example of many-to one relationship.You can see below diagram represent the many-to-one relationship between STUDENT and MAJOR.

Many-to-Many Relationship:-
A STUDENT can take many COURSE's and many STUDENT's can register for a given COURSE.In this example of Many-to-Many relationship.You can see below diagram represents the many-to-many relationship between STUDENT and COURSE.