We present an execution model for distributed transactions that can be employed for multidatabase systems. We use the Flex Transaction model that has been proposed as a highly general and flexible tool for the specification of distributed transactions and extend it by allowing nested and possibly recnrsive transaction specifications. We show how a given transaction specification and its execution model can be mapped into a representation in a new concurrent Prolog language, the VPL (Vienna Parallel Logic) language. The representation in VPL can be considered as an executable specification. We show some optimizations concerning this mapping and define a significant subclass of Flex Transactions with a declarative representation in VPL that can be modeled by AND/OK structures. We argue that it is more advantageous to use VPL directly for the transaction specification because it provides more flexibility and more control aspects than the Flex Transaction model.