COSPAN DPO APPROACH: AN ALTERNATIVE FOR DPO GRAPH TRANSFORMATIONS

The DPO approach for graph transformations is based on productions p = (L <- K -> R) and direct transformations defined by two pushouts, where, roughly spoken, in the first pushout all items in L\K are deleted and in the second one all items R\K are added, while those items in K are preserved. Intuitively, K is the intersection of L and R and, formally, p = (L <- K -> R) is a span of graph morphisms. In this paper, we consider productions (p) over bar = ( L -> (K) over bar <- R) which are cospans of graph morphisms, and (K) over bar corresponds to the union of L and R. As before, direct transformations are defined by double pushouts, but now the first pushout adds all items in (K) over bar \L and the second one deletes (K) over bar \R. This basic idea can be extended to an alternative graph transformation approach, called cospan DPO approach. Key notions of the classical DPO approach can be reformulated in the cospan DPO approach and our main result shows in which way corresponding concepts and results are equivalent.