Usually the new and updated records can be identified by a modification date (or maybe a record version number) field. If that's not available then you may be able to identify the new records by checking if the record identifier already exists. If it doesn't then it's a new record. Changed records can be identified by computing a hash of all the fields of the record and compare it to the hashes of all other records. But you really want to have a modification date (or record version number field as second choice). Insist on one if it doesn't exist yet.
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