Transaction Logic with External Actions

We propose External Transaction Logic (or ET R), an extension of Transaction Logic able to represent updates in internal and external domains whilst ensuring a relaxed transaction model. With this aim, ET R deals with two main components: an internal knowledge base where updates follow the strict ACID model, given by the semantics of Transaction Logic; and an exter- nal knowledge base of which one has limited or no control and can only execute external actions. When executing actions in the external domain, if a failure oc- curs, it is no longer possible to simply rollback to the initial state before executing the transaction. For dealing with this, similarly to what is done in databases, we define compensating operations for each external action to be performed to ensure a relaxed model of atomicity and consistency. By executing these compensations in backward order, we obtain a state considered to be equivalent to the initial one.