Rajesh,
OILM (with children tables ILM1 and ILM2) - it records all the information regarding the documents. It is pretty similar to OINM, but it records Sales and Purchase orders.
OIVL records the rows in a document, so 1 row in OIVL is one row in a document. ILV1 expands on the same information given by OIVL. In these tables there are information no matter which valuation method is used in the database.