Even though the Software Processing Model describes the actual operations performed on a package satisfactorily, the modelling of repository changes needs the introduction of a new concept. When a product maintainer has to change the version of a product that is InProduction, two state transitions must take place: (1) a first version is RemovedFromProduction, (2) a second one is IntroducedInProduction. Moreover, both operations should be executed in the right order and in an atomic way. Therefore, a transaction system was introduced in ASIS. A transaction is a sequence of operations (transitions and/or specific actions) that are all performed completely or at all.