Restrictive and Nonrestrictive Clause

Restrictive and Nonrestrictive Clause - What are the differences?

Restrictive Clause:

A restrictive clause carries information that classifies or categorizes a noun(s). It is called restrictive because if we remove that clause, there will be no reason for the sentence to exist. Example:

The students who were absent missed an important lecture. 
Here, 'who were absent' is a restrictive clause. It was used only to specify some absent students. This is obviously restrictive because if we say, "The students missed an important lecture." omitting  'who were absent', then the intended meaning will be lost. The sentence will be grammatically fine, but we will understand that some specific students missed a lecture not knowing what kind if students they were.   

Nonrestrictive Clause:

A nonrestrictive clause carries additional information about a noun(s). It is called nonrestrictive because if we omit it, there will be no problem in the structure or meaning of the sentence. A nonrestrictive clause starts after a comma or it is surrounded by commas. Since it doesn't categorize or classify the noun(s), we can understand that the noun(s) which is described by the nonrestrictive clause is exclusive, without any similar existence. Example:

Nobita, who was absent yesterday, missed an important lecture.
Here, 'who was absent yesterday' surrounded by two commas is a non-restrictive clause. If we omit it, the sentence "Nobita missed an important lecture." still makes a complete sense. The non-restrictive clause here is not classifying Nobita or separating him from a group of students, rather it is adding information. If we write: Nobita who was absent yesterday missed an important lecture, it will be incorrect or mean that there is more than one Nobita; one of them was absent.

Restrictive vs Nonrestrictive Clause:

A sentence can be formed with both restrictive and non-restrictive clause, but the meaning will be different.

Restrictive: I have a brother who goes to school. 

[I may have several brothers, and I am not specifying that I have just one brother. I am just saying that among my siblings(either brothers or sisters or both), one brother goes to school]

Nonrestrictive: I have a brother, who goes to school. 

[I have just one brother, and he goes to school]

Restrictive: I like children who are very cute= you like only cute children, but you don't like unattractive children
Nonrestrictive: I like children, who are very cute =you like all children, and all children are cute