Six thousand years ago, the Sumerians invented writing for transaction processing. The earliest known writing is found on clay tablets recording the royal inventory of taxes, land, grain, cattle, slaves, and gold; scribes evidently kept records of each transaction. ... The Sumerians' approach allowed the scribes to easily ask questions about the current and past state, while providing a historical record of how the system got to the present state. — Gray & Reuter
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