On algebra of languages representable by vertex-labeled graphs

In this paper, we introduce and study an algebra of languages representable by vertex-labeled graphs. The proposed algebra is equipped with three operations: the union of languages, the merging of languages and the iteration. In contrast to Kleene algebra, which is mainly used for edge-labeled graphs, it can adequately represent many properties of languages defined by vertex-labeled graphs and provides a natural translation from vertex-labeled graphs to regular expressions and vice versa.