Similarity Measure among Structures of Local Government Statute Books Based on Tree Edit Distance

A similarity measure between statute books of local governments that can help reveal suggestive similarities is proposed. The regulations of a local government are stored in a statute book, and they are categorized in a layered structure. The layered structure can be described as an ordered tree in computer science, and we define the similarity of statute books as the tree edit distance between two trees. We have calculated the similarities among statute books of the 47 Japanese prefectures and plotted them on a plane using multi-dimensional scaling. The results visually indicate the relationships of similarities among them, and there are several outlier prefectures and clusters. This will help find local governments with similar regulations, which will facilitate the writing or revision of statutes, especially in small local governments, which are typically short staffed.