Evaluate the similarity between them and classify them into classes from 0-5 as follows:
0 : The two sentences are completely dissimilar.
1 : The two sentences are not equivalent, but are on the same topic.
2 : The two sentences are not equivalent, but share some details.
3 : The two sentences are roughly equivalent, but some important information differs/missing.
4 : The two sentences are mostly equivalent, but some unimportant details differ.
5 : The two sentences are completely equivalent, as they mean the same thing.

Sentence 1: A young boy laying on a sofa with a dog. Sentence 2: A small boy laying on a sofa with a dog.
5

Sentence 1: Two die in Syria violence after UN monitors land Sentence 2: Two year doping ban for Contador
0

Sentence 1: Nirvana is very different than oblivion. Sentence 2: Nirvana is NOT oblivion.

4