Logics for Unranked Trees: An Overview

TL;DR

This paper surveys various logical languages for unranked trees, such as XML models, focusing on their expressive power, automata relations, and model-checking properties, highlighting differences between ordered and unordered trees.

Contribution

It provides a comprehensive overview of existing logics for unranked trees, comparing their purposes, automata models, and computational properties.

Findings

Different logics suit data extraction and navigation tasks.

Logics vary in automata models and model-checking complexity.

Ordered and unordered trees exhibit distinct logical behaviors.

Abstract

Labeled unranked trees are used as a model of XML documents, and logical languages for them have been studied actively over the past several years. Such logics have different purposes: some are better suited for extracting data, some for expressing navigational properties, and some make it easy to relate complex properties of trees to the existence of tree automata for those properties. Furthermore, logics differ significantly in their model-checking properties, their automata models, and their behavior on ordered and unordered trees. In this paper we present a survey of logics for unranked trees.