Source System

A source system is a system from which a particular data flow obtains records. It is often the application where business activity is recorded, such as an ordering system. The term is relative to the flow: a warehouse can be the source for an export even though it did not create the original transactions.

Find where the fact was recorded

Suppose a customer orders a book through a website. The order service records the order, the payment provider records a charge, and the delivery service records shipment. Each is a source for different facts. An order being placed does not by itself prove that payment settled or that the book shipped.

For this example, define which system is authoritative for each question. A system of record is the designated authority for a particular fact; it need not be the source currently being read. A copied file may be convenient while lagging behind that authority.

A source can contain mistakes

Ingestion brings records from the source into another environment. It does not verify that a customer entered the right address or that an operator recorded the right quantity.

Source-to-target validation, such as the comparisons documented by AWS DMS, checks whether a transfer preserved data. Agreement with a source is different from proof that the source reflects reality. Both the transfer and the original recording process may need checks.

Reference: AWS DMS: Data validation.