A parameterized graph transformation calculus for finite graphs with monadic branches

  • Authors:

  • Kazuyuki Asada;Soichiro Hidaka;Hiroyuki Kato;Zhenjiang Hu;Keisuke Nakano

  • Affiliations:

  • The University of Tokyo;National Institute of Informatics;National Institute of Informatics;National Institute of Informatics;The University of Electro-Communications

  • Venue:
  • Proceedings of the 15th Symposium on Principles and Practice of Declarative Programming
  • Year:
  • 2013

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Abstract

We introduce a lambda calculus λTFG for transformations of finite graphs by generalizing and extending an existing calculus UnCAL. Whereas UnCAL can treat only unordered graphs, λTFG can treat a variety of graph models: directed edge-labeled graphs whose branch styles are represented by monads T. For example, λTFG can treat unordered graphs, ordered graphs, weighted graphs, probability graphs, and so on, by using the powerset monad, list monad, multiset monad, probability monad, respectively. In λTFG, graphs are considered as extension of tree data structures, i.e. as infinite (regular) trees, so the semantics is given with bisimilarity. A remarkable feature of UnCAL and λTFG is structural recursion for graphs, which gives a systematic programming basis like that for trees. Despite the non-well-foundedness of graphs, by suitably restricting the structural recursion, UnCAL and λTFG ensures that there is a termination property and that all transformations preserve the finiteness of the graphs. The structural recursion is defined in a "divide-and-aggregate" way; "aggregation" is done by connecting graphs with ε-edges, which are similar to the ε-transitions of automata. We give a suitable general definition of bisimilarity, taking account of ε-edges; then we show that the structural recursion is well defined with respect to the bisimilarity.