1. A method for validating data changes made to a database, wherein the changes are made in the context of a transaction, using a rules database storing a plurality of rules, the method comprising: identifying a set of data entities affected by one or more data changes made in the context of the transaction; in response to an instruction to commit the transaction, validating data entities in the set of affected data entities using rules from the rules database; and committing the transaction in dependence on the outcome of the validation.