"Relational Data Model" is the most used data model because it data independence. So "what is data independence now?".
Answer is if a database system is not multi-layered, then it becomes difficult to make any changes in the database system. Hence, Database systems are designed in multi-layers so the term data independence comes.

A database system normally contains a lot of data in addition to users’ data. For example, it stores data about data, known as metadata, to locate and retrieve data easily. It is rather difficult to modify or update a set of metadata once it is stored in the database. But as a DBMS expands, it needs to change over time to satisfy the requirements of the users. If the entire data is dependent, it would become a tedious and highly complex job.

Ok! Now continue with our topic . So in database data is stored in simple data structure Table: This provides logical and physical data independence and physical storage independence.

Guys what if i tell you there can be substitute or an alternative for relational data model. Yes! you heard it right. It is called "Entity Relationship Model".

It proposes thinking of a database as a collection of data rather than being used as a model on its own.

The ER model is used as a tool to design relational databases. In ER model, entities are objects that exist independently of any other entities in the database.
There are two building blocks of ER Diagram: 1)"Entity": It is noun that can be person, place or thing and can be drawn as rectangle.
2)"Attributes": Entities have attributes which are the data elements that characterize the entity. It tells us more about entity. Drawn as Oval shape.

An example for this two building blocks can be given as BOOK(entity or table name) and price, title, author and description are its attributes(columns names in table BOOK).

Each table is assigned a "primary key" which uniquely identifies each tuple or row in a table, preventing duplication of data and providing a way of defining relationship between tables.

Table can also contain "foreign key" which are primary key defined in other tables, creating a link between the tables.

In next post we will try to understand about basic sql statements.