Answer:
The answer to this question is given below in this explanation section.
Step-by-step explanation:
In the relationship model of database a primary key is a specific choice of a minimal set of attributes that uniquely specific a tuple in a relation.Informally a primary key is which attribute and in simple cases are simple a single attribute.More formally a primary key is a choice of candidate key any other candidate key is an alternate key.
A primary key may consists of real word observable in which way it is called natural key,while an attribute created to function as a key and not use for identification outside the database is called a surrogate key.For example for a database of people time and location of birth could be a natural key.National identification number is another example of an attribute that may be used as an natural key.