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Relational Model in DBMS

Last Updated : 04 Feb, 2024
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E.F. Codd proposed the relational Model to model data in the form of relations or tables. After designing the conceptual model of the Database using ER diagram, we need to convert the conceptual model into a relational model which can be implemented using any RDBMS language like Oracle SQL, MySQL, etc. So we will see what the Relational Model is.

The relational model uses a collection of tables to represent both data and the relationships among those data. Each table has multiple columns, and each column has a unique name. Tables are also known as relations. The relational model is an example of a record-based model. Record-based models are so named because the database is structured in fixed-format records of several types. Each table contains records of a particular type. Each record type defines a fixed number of fields, or attributes. The columns of the table correspond to the attributes of the record type. The relational data model is the most widely used data model, and a vast majority of current database systems are based on the relational model.

What is the Relational Model? 

The relational model represents how data is stored in Relational Databases. A relational database consists of a collection of tables, each of which is assigned a unique name. Consider a relation STUDENT with attributes ROLL_NO, NAME, ADDRESS, PHONE, and AGE shown in the table. 

Table Student

1 RAM DELHI 9455123451 18
2 RAMESH GURGAON 9652431543 18
3 SUJIT ROHTAK 9156253131 20


Important Terminologies

  • Attribute: Attributes are the properties that define an entity. e.g.; ROLL_NO, NAME, ADDRESS
  • Relation Schema: A relation schema defines the structure of the relation and represents the name of the relation with its attributes. e.g.; STUDENT (ROLL_NO, NAME, ADDRESS, PHONE, and AGE) is the relation schema for STUDENT. If a schema has more than 1 relation, it is called Relational Schema.
  • Tuple: Each row in the relation is known as a tuple. The above relation contains 4 tuples, one of which is shown as:
1 RAM DELHI 9455123451 18
  • Relation Instance: The set of tuples of a relation at a particular instance of time is called a relation instance. Table 1 shows the relation instance of STUDENT at a particular time. It can change whenever there is an insertion, deletion, or update in the database.
  • Degree: The number of attributes in the relation is known as the degree of the relation. The STUDENT relation defined above has degree 5.
  • Cardinality: The number of tuples in a relation is known as cardinality. The STUDENT relation defined above has cardinality 4.
  • Column: The column represents the set of values for a particular attribute. The column ROLL_NO is extracted from the relation STUDENT.





  • NULL Values: The value which is not known or unavailable is called a NULL value. It is represented by blank space. e.g.; PHONE of STUDENT having ROLL_NO 4 is NULL. 
  • Relation Key: These are basically the keys that are used to identify the rows uniquely or also help in identifying tables. These are of the following types.

Constraints in Relational Model

While designing the Relational Model, we define some conditions which must hold for data present in the database are called Constraints. These constraints are checked before performing any operation (insertion, deletion, and updation ) in the database. If there is a violation of any of the constraints, the operation will fail.

Domain Constraints

These are attribute-level constraints. An attribute can only take values that lie inside the domain range. e.g.; If a constraint AGE>0 is applied to STUDENT relation, inserting a negative value of AGE will result in failure.

Key Integrity

Every relation in the database should have at least one set of attributes that defines a tuple uniquely. Those set of attributes is called keys. e.g.; ROLL_NO in STUDENT is key. No two students can have the same roll number. So a key has two properties: 

  • It should be unique for all tuples.
  • It can’t have NULL values.

Referential Integrity

When one attribute of a relation can only take values from another attribute of the same relation or any other relation, it is called referential integrity. Let us suppose we have 2 relations 

Table Student 

1 RAM DELHI 9455123451 18 CS
2 RAMESH GURGAON 9652431543 18 CS
3 SUJIT ROHTAK 9156253131 20 ECE

Table Branch 


BRANCH_CODE of STUDENT can only take the values which are present in BRANCH_CODE of BRANCH which is called referential integrity constraint. The relation which is referencing another relation is called REFERENCING RELATION (STUDENT in this case) and the relation to which other relations refer is called REFERENCED RELATION (BRANCH in this case). 

Anomalies in the Relational Model

An anomaly is an irregularity or something which deviates from the expected or normal state. When designing databases, we identify three types of anomalies: Insert, Update, and Delete.

Insertion Anomaly in Referencing Relation

We can’t insert a row in REFERENCING RELATION if referencing attribute’s value is not present in the referenced attribute value. e.g.; Insertion of a student with BRANCH_CODE ‘ME’ in STUDENT relation will result in an error because ‘ME’ is not present in BRANCH_CODE of BRANCH. 

Deletion/ Updation Anomaly in Referenced Relation: 

We can’t delete or update a row from REFERENCED RELATION if the value of REFERENCED ATTRIBUTE is used in the value of REFERENCING ATTRIBUTE. e.g; if we try to delete a tuple from BRANCH having BRANCH_CODE ‘CS’, it will result in an error because ‘CS’ is referenced by BRANCH_CODE of STUDENT, but if we try to delete the row from BRANCH with BRANCH_CODE CV, it will be deleted as the value is not been used by referencing relation. It can be handled by the following method: 

On Delete Cascade

It will delete the tuples from REFERENCING RELATION if the value used by REFERENCING ATTRIBUTE is deleted from REFERENCED RELATION. e.g.; For, if we delete a row from BRANCH with BRANCH_CODE ‘CS’, the rows in STUDENT relation with BRANCH_CODE CS (ROLL_NO 1 and 2 in this case) will be deleted. 

On Update Cascade

It will update the REFERENCING ATTRIBUTE in REFERENCING RELATION if the attribute value used by REFERENCING ATTRIBUTE is updated in REFERENCED RELATION. e.g;, if we update a row from BRANCH with BRANCH_CODE ‘CS’ to ‘CSE’, the rows in STUDENT relation with BRANCH_CODE CS (ROLL_NO 1 and 2 in this case) will be updated with BRANCH_CODE ‘CSE’.

Super Keys

Any set of attributes that allows us to identify unique rows (tuples) in a given relationship is known as super keys. Out of these super keys, we can always choose a proper subset among these that can be used as a primary key. Such keys are known as Candidate keys. If there is a combination of two or more attributes that are being used as the primary key then we call it a Composite key.

Codd Rules in Relational Model

Edgar F Codd proposed the relational database model where he stated rules. Now these are known as Codd’s Rules. For any database to be the perfect one, it has to follow the rules.

For more, refer to Codd Rules in Relational Model.

Advantages of the Relational Model

  • Simple model: Relational Model is simple and easy to use in comparison to other languages.
  • Flexible: Relational Model is more flexible than any other relational model present.
  • Secure: Relational Model is more secure than any other relational model.
  • Data Accuracy: Data is more accurate in the relational data model.
  • Data Integrity: The integrity of the data is maintained in the relational model.
  • Operations can be Applied Easily: It is better to perform operations in the relational model.

Disadvantages of the Relational Model

  • Relational Database Model is not very good for large databases.
  • Sometimes, it becomes difficult to find the relation between tables.
  • Because of the complex structure, the response time for queries is high.

Characteristics of the Relational Model

  • Data is represented in rows and columns called relations.
  • Data is stored in tables having relationships between them called the Relational model.
  • The relational model supports the operations like Data definition, Data manipulation, and Transaction management.
  • Each column has a distinct name and they are representing attributes.
  • Each row represents a single entity. 

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