%0 Journal Article %T Graph inverse semigroups: their characterization and completion %A David G. Jones %A Mark V. Lawson %J Mathematics %D 2011 %I arXiv %X Graph inverse semigroups generalize the polycyclic inverse monoids and play an important role in the theory of C*-algebras. This paper has two main goals: first, to provide an abstract characterization of graph inverse semigroups; and second, to show how they may be completed, under suitable conditions, to form what we call the Cuntz-Krieger semigroup of the graph. This semigroup is the ample semigroup of a topological groupoid associated with the graph, and the semigroup analogue of the Leavitt path algebra of the graph. %U http://arxiv.org/abs/1106.3644v2