when two noun sitting beside each other indicate the same person or thing is an appositive or case in apposition. There should be put comma before and after the appositive.it is used as a noun phrase.it is of three kinds.such as
1)Nominitive in appositive: used after the subject.i.e.Mr.kamal,headmaster of this school, is very honest.
2)Objective in appositive: used after the object to express more about the object.i.e.I know Jamal ,an honest boy.
3)possessive in adjective: the possessive to indicate the possession with its previous noun.i.e.I know Nazru,the poet's work.
The appositive used at first of a sentence sits before the noun.i.e.The famous novel,David copperfield is a classic.