How can U create or import flat file definition in to the warehouse designer?

U can not create or import flat file definition in to warehouse designer directly. Instead U must analyze the file in source analyzer, and then drag it into the warehouse designer. When u drags the flat file source definition into warehouse designer workspace, the warehouse designer creates a relational target definition not a file definition. If u want to load to a file, configure the session to write to a flat file. When the informatica server runs the session, it creates and loads the flat file