1. Table : In relational data model , data is stored in the tables. The tables consists of a number of rows and columns. Thus, table is used because it can represent the data in the most simplest form possible making data retrieval very easy.
2. Attribute : Any relation have definite properties that are called as attributes.
3. Tuple : Rows of table represents the tuple which contains the data records.
4. Domain : Domain is a set of values which is indivisible i.e. value for each attribute present in the table contains some specific domain in which the value needs to lie. For Example : The value of date of birth must be greater than zero. As, it cannot be negative. This is called domain of an attribute.
5. Relation : A relation in relational data model represents the respective attributes and the correlation among them.
Any relation can be denoted by : R(A1, A2, A3,…,An)
where, R Represents relation name and A1, A2, A3,…,An represents the attributes present in the relation.
1. Domain Constraint : This constraint is mainly applicable on the value of attributes present in the table. It ensures that the values are legitimate and comes within a pre-specified domain.
For example : Name of a person cannot contain digits (0 to 9) or special characters and Age of a person cannot be negative.
2. Key Constraint : The key constraint ensures that a table representing a relation, any row/tuple can be fetched directly using a single unique attribute called as a key. There might be a situation where, combination of multiple attribute may act as a key also.
For example : Consider a relation R(Roll No, Class, marks, Age) having some attribute. If we want to fetch the details of any student, with the help of a key it can be done.
3. Referential Integrity Constraint : The referential integrity works on the concept of foreign key. A foreign key is nothing but an attribute that is commonly linked between two relation using that same attribute. Both the relations/tables must contain the same attribute.
For example : Consider two relations R1(Roll No, Name, Marks) and R2(Roll No, Address, Age) of students of a school. Roll No being the common attribute will act as a key for relation R1 and can reference to Roll No attribute of relation R2 with the help of which any tuple can be retrieved from the tables.