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
- Entity-Relationship Model ( ERD Diagrams )
- 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 .
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
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 .
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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