Need of Data Migration or Data Conversion

Need of Data Migration or Data Conversion,
Migration/Conversion are required when we are upgrading to one version to another (e.g. Oracle Apps 11.5.7 to Oracle 11.5.10) or moving data from some legacy system to Oracle Apps. There will be bulk  of data (sometimes millions or even more than that) that needs to be moved from one system to another  and  before moving the data it should be validated and only valid records should be entered into Oracle Apps.

If both the systems (Target and source) are not having same structure for data (Tables are not same/Table Structure is not same/The data is being stored in database is not same), it needs to be translated (e.g. upgrading from Oracle 11i to R12 where table structures are not same) then we say it as conversion (any kind of translation of data on Source data to make it suitable for Target system) otherwise migration.