Transactional graph transformation systems (t-gtss) have been recently proposed as a mild extension of the standard dpo approach to graph transformation, equipping it with a suitable notion of atomic execution for computations. A typing mechanism induces a distinction between stable and unstable items, and a transaction is defined as a shift-equivalence class of computations such that the starting and ending states are stable and all the intermediate states are unstable. The paper introduces an equivalent, yet more manageable definition of transaction based on graph processes. This presentation is used to provide a universal characterisation for the class of transactions of a given t-gts. More specifically, we show that the functor mapping a t-gts to a graph transformation system having as productions exactly the transactions of the original t-gts is the right adjoint to an inclusion functor.
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