Output-sensitive autocompletion search

Holger Bast, Christian W. Mortensen, Ingmar Weber

Research output: Contribution to journalArticle

16 Citations (Scopus)


We consider the following autocompletion search scenario: imagine a user of a search engine typing a query; then with every keystroke display those completions of the last query word that would lead to the best hits, and also display the best such hits. The following problem is at the core of this feature: for a fixed document collection, given a set D of documents, and an alphabetical range W of words, compute the set of all word-in-document pairs (w, d) from the collection such that w W and d D. We present a new data structure with the help of which such autocompletion queries can be processed, on the average, in time linear in the input plus output size, independent of the size of the underlying document collection. At the same time, our data structure uses no more space than an inverted index. Actual query processing times on a large test collection correlate almost perfectly with our theoretical bound.

Original languageEnglish
Pages (from-to)269-286
Number of pages18
JournalInformation Retrieval
Issue number4
Publication statusPublished - 1 Aug 2008



  • Autocompletion
  • Index data structure
  • Output-sensitive
  • Prefix search

ASJC Scopus subject areas

  • Information Systems
  • Library and Information Sciences

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