Technical Perspective: Optimizing Tree Patterns for Querying Graph- and Tree-Structured Data

From the early days of databases, practitioners and researchers have pursued techniques for rewriting queries into equivalent ones that are easier to evaluate. The following paper closes a fundamental gap that we have had in our understanding of this challenge in the context of tree patterns. Such patterns are common and basic components of query languages for graph and tree data such as SPARQL, Cypher and XQuery. The authors study the question of whether the given tree pattern can be replaced with a smaller one, the question of whether it involves redundant conditions, and most importantly, the relationship between these two questions.