Techniques are provided for extending a business transaction framework to support user-provided compensation logic for business transactions. The extensibility framework may be used to implement user-defined semantics for (a) validating concurrent updates to shared data and (b) performing compensating actions when an associated transaction is aborted. In one embodiment, the extensibility and the compensation are provided at the data-type level. User-provided logic also maintains summaries that include values that are externalized so that they may be referenced in user-provided operational constraints.