The authors present a transaction management model to unify concurrency control and recovery for databases with an arbitrary but finite set of operations. The model generalizes previous work [1] by defining transactions on data objects of different abstract data types. The correctness criterion provided for the unified transaction model ensures both serializability and atomicity for transactions over semantically rich operations. Although the paper is theoretical, it is well written and comprehensive, and thus easy to follow for anyone with a background in concurrency control theory. The illustrative examples facilitate understanding of the theoretical discussions. The paper makes a meaningful contribution to database theory.