This just sequence of my previous post……
I posted it in oracle forum.
As per Justin Cave an Oracle ACE Member:
You can certainly build a data warehouse (or any other type of database) without using a relational database. Whether you ought to do such a thing, however, is another question.
Relational databases provide a lot of functionality that facilitates building data warehouses (or other types of data-driven applications), but other tools could certainly do the same thing. Organizations were building data warehouses before relational databases were invented, though not many would try to build a data warehouse using VSAM files on a mainframe today.