Data Modelling | Database Management Systems

Database Management Systems are designed to store information and data for softwares . Before , implementation of the system the DBMS is logically structured and designed. This decides how data will be stored , processed and interact.

We studied about proposed data models previously and last of it was relational database which is being mostly used in industry now .  Once business analyst collects requirements from client with careful and elaborate discussions ,Data Models are defined . The discussion leads to decisions about the business logic .
Data Modelling comes in pretty much handy in implementing those decisions . Think of data modelling as a road map into your software solution.

Concluding above discussion and a simple definition for Data Modelling could be :

 The logical structure of a database and  determining the manner in which is  stored, organised and manipulated

Two Data Models are

  1. Entity-Relationship Model ( ERD Diagrams ) 
  2. Relational Model 

Both of these models are very helpful to draw the road map for software dbms. Let’s go through an overview for both .

ENTITY-RELATIONSHIP MODEL

This model is designed by translating real-world scenarios into database model by creating  entities ,  relationships ,  attributes and constraints.  All of these terms have detail articles. Click the above links for details. This is a conceptual diagram of a database . Designer creates entities , attributes and define relationships between them and constraints to manage them

   Entity & Members

Entities ( real-world ) objects and their attributes (properties ) . Example Student is an entity and his Name , age , address , gender etc are attributes

   Relationships

The logical association and way of interaction between entities enforced by using cardinalities and modalities . Example Student studies in a University . When we link them we need to define how should they interact. Meaning is how many students can be in a university at maximum and minimum .

  • One-to-One
  • One-to-Many
  • Many-to-Many
  • Many-to-One

This is all linked together by Crow’s Foot Notation .  Check a sample ERD for a University Management System

 

RELATIONAL MODEL :

This model is more scientific and therefore , used very widely and practically in the industry . Here entities are known as relation/table . Attributes/members are converted into columns.
Every members has its own domain data in it.

Pictures speaks louder than words . See below for the explanation :

 

Table : Relation also  referred as entity in ERD Model

Attributes : Properties of entities

Columns :   For storing attribute data

Rows      :   For unique data against all attributes

 

This relations in a DBMS are usually combine together by Joins , Normalised and constraints for reporting , storage and support of application. Since  they are the biggest and most important concepts in whole DBMS therefore , We will explain this in detailed articles .

An example for Relational Model given below. We have used same example which we used in ERD .

Here we define attribute name with the data type and relationship between them with cardinality and modality.

 

In future , we will take a case study . We will go through a user requirement and translate it into ERD and relational model . Normally , both these models are applied to have a better and a clear understanding for both technical and non-technical staff .

Then we will see about normalisation and  use same example of ERD and apply normalization on it.  By the end of this series  , you will be able to translate the complete user requirement into database management system.

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Cheers!

 

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