Which Classification Scheme is being used in the World Libraries?

Dewy Decimal Classification is widely used in the world due to its simplicity and easiness. 

Dewey Decimal Classification and Library of Congress Classification.

Dewy Decimal Classification

and Library of Congress Classification Schemes are mostly used in the world

Dewey Decimal Classification-  22nd Edition

In Arab World they Usually Use Dewey Decimal Classification (DDC), and in the Most world, and in other they Use Classification for Library of Congress

Dewey Decimal Classification

Dewey Decimal Classification Scheme (DDC)

Library of Congress Scheme