Relation Data Model in DBMS
The relational data model is the most common data model, and it is used for data storage and processing all around the world. This model is easy to understand and contains all of the traits and capabilities needed to process data efficiently.
Let’s learn some new concepts-
Tables: Tables are the format in which relations are saved in a relational data model. Rows and columns make up a table, with rows representing records and columns representing attributes.
Tuple: A tuple is a single row in a table that contains a single record for a given relation. Relation instance: In a relational database system, a relation instance is a finite set of
tuples. There are no duplicate tuples in relation instances.
Relation schema: A relation schema specifies the name of the relation (table name), as well as the characteristics and their names.
Relation key: Each row has one or more qualities known as a relation key that can uniquely identify the row in the relation (table).
Attribute domain: Every attribute has a pre-defined value scope, which is known as the attribute domain.
CONSTRAINTS-
For a relationship to be valid, it must satisfy certain requirements. Relational Integrity Constraints are the name for these conditions. Three main integrity restrictions exist.
1. Domainconstraints 2. Key constraints
3. Referential integrity constraints 1. Domain Constraints-
• A domain constraint defines an attribute's domain, or set of values, and specifies that the attribute's value must be the atomic value from its domain.
Consider the following Student table-
| STU_ID | Name | Age |
| S001 | Akshay | 20 |
| S002 | Abhishek | 21 |
| S003 | Shashank | 20 |
| S004 | Rahul | A |
Here, value ‘A’ is not allowed since only integer values can be taken by the age attribute.
2.Key Constraint-
Key constraint specifies that in any relation-
• All the values of primary key must be unique. • The value of primary key must not be null.
Example-
Consider the following Student table-
|
STU_ID |
Name |
Age |
| S001 | Akshay | 20 |
| S001 | Abhishek | 21 |
| S003 | Shashank | 20 |
| S004 | Rahul | 20 |
This relation does not satisfy the key constraint as here all the values of primary key are not unique.
3.Referential Integrity Constraint-
• This constraint is enforced when a foreign key references the primary key of a relation.
• It specifies that all the values taken by the foreign key must either be available in the relation of the primary key or be null.