Answer:   Flat file schema is a blueprint which have rules for the flat file. IS will validate the flat file against this Flat file schema.Flat file scheme can be used to validate the incoming flat files.
Schema provides definition for flat files against which IS can validate flatfiles
Flat file schemas serve two purposes. They define all of the same record and field characteristics (including structure) as XML schemas, and they provide a mechanism for defining all of the flat file characteristics that are required to translate a flat file instance message into an equivalent XML instance message (or vice versa).