[pkd]

SQL or not doesn't really matter. Double entry provides redundancy, and redundancy allows for auditing. It's like checksumming to detect errors.

[dataflow]

I guess I'm asking: what would go wrong with the design in my comment, which makes transactions first-class and has a single entry for each one? What errors would double entry prevent that this doesn't?

[namaria]

You offered no design. Db schema has nothing to do with transaction guarantees.