Data Models in DBMS | Data Modeling in RDBMS

Data Modeling is the process of creating a data model for the data to be stored in a database. Data models define how data is connected to each other and how they are processed and stored inside the system.

A database model defines the logical design and structure of a database. The data models are used to show how data is stored, accessed and updated in the database management system. 

Data Model is like an architect’s building plan, which helps to build conceptual models and set a relationship between data items.

 There are many kinds of data models. The most popular data models are:

• Relational Data Model
• Hierarchical data Model
• Network Data Model
• Entity–relationship model

Relational Data Model:

Relational Model is the most widely used model. In this model, data is organized in two-dimensional tables and the relationship is maintained by storing a common field.

This model was introduced by E.F Codd in 1970, and since then it has been the most widely used database model.

The basic structure of data in the relational model is tables. All the information related to a particular type is stored in rows of that table.

Hence, tables are also known as relations in relational model.

The main highlights of this model are:

• Data is stored in tables called relations.
• Relations can be normalized.
• In normalized relations, values saved are atomic values.
• Each row in a relation contains a unique value.
• Each column in a relation contains values from a same domain.

Hierarchical Data Model:

This model organizes the data into a  tree like structure with a single root to which all the other data is linked. The hierarchy starts from the root data, and expands like a tree, adding child nodes to the parent nodes. In this model, a child node will only have a single parent node.

In this database model, there exists a one-to-many relationship among data. 

The hierarchical model is based on the parent-child hierarchical relationship. In this model, there is one parent entity with several children entity. At the top, there should be only one entity which is called root. For example, an organization is the parent entity called root and it has several children entities like clerk, officer, and many more.

Network Data Model:

In the network model, data is organized in the form of a graph. This model is an extension of the hierarchical model. It replaces the hierarchical tree with a graph, and allowed to have more than one parent node.

In the network model, each record in the database can have multiple parents, i.e. the relationships among data elements can have a many to many relationship.

In the network database model, the records are connected to each other. In this manner, the hierarchy is maintained among the records. 

Entity-Relationship Model:

Entity-Relationship (ER) Model is based on the notion of real-world entities and relationships among them. While formulating real-world scenario into the database model, the ER Model creates entity set, relationship set, general attributes and constraints.

ER Model is best used for the conceptual design of a database.

We use the ER diagram as a visual tool to represent an ER Model. ER diagram has the following three components:

• Entity: Entity is a real-world thing. It can be a person, place, or even a concept. Example: Teachers, Students, Course, Building, Department, etc are some of the entities of a School Management System.
• Attributes: An entity contains a real-world property called attribute. This is the characteristics of that attribute. Example: The entity teacher has the property like teacher id, salary, age, etc.
• Relationship: The logical association among entities is called relationship. Relationships are mapped with entities in various ways. Mapping cardinalities define the number of association between two entities.

Mapping cardinalities −

• one to one
• one to many
• many to one
• many to many