While reading about OBIEE architecture it mentioned that end user's request is converted in to Logical SQL by presentation layer and BI server component change the Logical SQL to Physical SQL.
What is the difference in Logical and Physical SQL?
What's also important to note and remember is the reason for this distinction which also explains the two concepts:
Logical SQL is source-agnostic and nothing but a "Logical Structured Query Language" (vs "SQL" the bespoke language itself). That means the BI servers gets a request in logical SQL, based on the originating analysis.
That logical SQL is then transformed depending on the source or sources underlying the model(s) required to fulfill the request. That transformation then produces the effective physical SQL or any language necessary like MDX for Essbase cubes or other (native) code for reading from XML files etc.
The logical SQL does not contain any source specifics. It doesn't distinguish between relational SQL-speaking databases, Essbase cubes, Hadoop sources, XML files etc. It's a unified, logical model/querying language rather than a specific, native source language.