Earliest Query Answering for Deterministic Stepwise Hedge Automata

Abstract

Earliest query answering (EQA) is the problem to enumerate certain query answers on streams at the earliest events. We consider EQA for regular monadic queries on hedges or nested words defined by deterministic stepwise hedge automata (dShas). We present an EQA algorithm for dShas that requires time O(c m) per event, where m is the size of the automata and c the concurrency of the query. We show that our EQA algorithm runs efficiently on regular XPath queries in practice.