Relational Model Concept
Relational model refers to any table with rows and columns. Each row of the table is called a tuple, and each column has a name, also known as an attribute.
Domain: It consists of some atomic values of a particular attribute.
Attribute: It is the name given to a particular column in a table. Each attribute Ai is required to have a domain, dom(Ai).
Relation instance: The relation instance constitutes of a limited set of tuples in the relational database system. There are no duplicate tuples in relation instances.
Relational schema: The relation name and columns names are present in a relational schema.
Relational key: All rows have either one or more than one attributes in the relational key. It is useful in identifying the rows in the relation.
Example: EMPLOYEE Relation
|
Employee ID |
Name |
Phone |
Designation |
Work Experience |
|
145 |
Rohit |
8981726920 |
HR |
1 year |
|
123 |
Sameer |
7868273674 |
Manager |
3 years |
|
178 |
Neha |
9282738489 |
Personal Secretary |
6 months |
|
134 |
Ravi |
9872628393 |
Editor |
2 years |
|
123 |
Asha |
9873637288 |
Engineer |
2 years |
- In the table given above, Employee ID, Name, Phone, Designation, and Work Experience are the attributes for a given column.
- The instance of schema EMPLOYEE consists of 5 tuples.
- t2= <123, Sameer, 7868273674, Manager, 3 years>
Features of Relation
- Name of the relation is different from all other relations.
- There is only one atomic value in each relation cell.
- There is a distinct name given to each attribute.
- There is no significance of the attribute domain.
- No duplicate value is there for any tuple.
- A different sequence can be used for the order of tuple.