To build on this, Datomic includes a pre-commit conflict check that would prevent this particular example from committing at all: it detects that there are two incompatible assertions for the same entity/attribute pair, and rejects the transaction. We think this conflict check likely prevents many users from actually hitting this issue in production.

The issue we discuss in the report only occurs when the transaction expands to non-conflicting datoms--for instance:

[Stu favorite-number 41]

[Stu hates-all-numbers-and-has-no-favorite true]

These entity/attribute pairs are disjoint, so the conflict checker allows the transaction to commit, producing a record which is in a logically inconsistent state!

On the documentation front--Datomic users could be forgiven for thinking of the elements of transactions as "operations", since Datomic's docs called them both "operations" and "statements". ;-)