The Logical(or conceptual) level shows how users interpret the relation
schemas and the meaning of their attributes. Having good relation 
schemas at this level enables users to understand clearly the meaning 
of the data in the relations, and hence to formulate their queries 
correctly.

The implementation(or storage) level , showing how the tuples in a base
relation are stored and updated. This level applies to schemas of base 
relations, which will be physically stored as files, whereas at a 
logical level we are interested in schemas of both base relations and 
views(virtual relations).