What if all transactions required strict global consistency? by Matthew Aslett.
From the post:
My mum recently moved house. Being the dutiful son that I am I agreed to help her pack up her old house, drive to her new place and help unpack when we got there.
As it happens the most arduous part of the day did not involve packing, driving or unpacking but waiting: waiting for the various solicitors involved to confirm that the appropriate funds had been deposited in the appropriate bank accounts before the estate agents could hand over the keys.
It took hours, and was a reminder that while we might think of bank transfers as being instantaneous, there can be considerable delays involved in confirming that the correct amount has been debited from one bank account and credited to another.
Matthew goes on to illustrate that banking transactions have always been “eventually consistent.” He doesn’t mention it but the the Uniform Commercial Code has several sections that cover checks, bank deposits and other matters. Text of the UCC at LLI.
The one thing the financial industry has that topic maps lack, is a common expectation of “eventual consistency.” The Uniform Commercial Code establishes (where adopted) the rules by which “eventual consistency” for banks is governed.
To avoid client disappointment, discuss “eventual consistency” up front. If your client expects instantaneous merging, with some data sets, they are likely to be disappointed.
The saying about a project being completed: faster, cheaper, better, but you can only pick two out of the three? Works with merging as well.