Relational Data Model

Terms used in the relational model

Relation:

• Representing data in the form of a table consisting of rows and columns and relation both convey the same meaning.
• Student  is a relation which consists of student records.

Schema:

• Schema is nothing but the organization of data in a table i.e in what order  the data is logically aligned 
• STUDENT relation can be represented as  STUDENT (STUD_ID, NAME, PHONE, STATE, STUD_AGE).

Instance:

• Set of unique values present in the table at present is known as relational instance.

Attribute:

• An attribute defines the properties of a table that means what type of data that a table is storing ,these are nothing but a view of data in the form of columns
• In the relation student STUD_ID, NAME, PHONE, STATE, STUD_AGE correspond to the attributes of the relation.

Domain :

• A domain is nothing but the set of possible values that are allowed for a column in a database table
• For example, the age column in the student table is allowed to have values between 21 -32.

Tuple :

• It is nothing but the row of the database table
• The student relation is having 4 tuples or rows.

Null values :

• There are certain situations where data may be unknown, missing or undefined which are represented by using this NULL
• A null value is different from zero and any operation on null value will result in null.

Advantages of the relational model

• Data integrity for accuracy and consistency 
• No data redundancy 
• Access control and integrity in the form of constraints which enables validation before entering and accessing the data 
• Provides high security 
• Supports to store any types(numbers, characters, date, images, audio, text files )
• Data can be managed and used by several users at a time 
• Data can be shared across several platforms.