Compact labeling schemes for ancestor queries

Serge Abiteboul*, Haim Kaplan, Tova Milo

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review


We consider the following problem. Give a rooted tree T, label the nodes of Tin the most compact way such that given the labels of two nodes one can determine in constant time, by looking only at the labels, if one node is an ancestor of the other. The best known labeling scheme is rather straightforward and uses labels of size at most 2 log n, where n is the number of vertices In the tree. Our main result in this paper is a labeling scheme with maximum label size close to 3/2 log n. Our motivation for studying this problem is enhancing the performance of Web search engines. In the context of this application each indexed document is a tree and the labels of all trees are maintained in main memory. Therefore even small improvements in the maximum label size are important. There are no lower bounds known for this problem except for an obvious lower bound of log n that follows from the fact that different vertices must have different labels. The guestion whether one can find even shorter labels remains an intriguing open guestion.

Original languageEnglish
Title of host publicationProceedings of the 12th Annual ACM-SIAM Symposium on Discrete Algorithms
Number of pages10
StatePublished - 2001
Event2001 Operating Section Proceedings, American Gas Association - Dallas, TX, United States
Duration: 30 Apr 20011 May 2001

Publication series

NameProceedings of the Annual ACM-SIAM Symposium on Discrete Algorithms


Conference2001 Operating Section Proceedings, American Gas Association
Country/TerritoryUnited States
CityDallas, TX


  • Algorithms
  • Theory
  • Verification


Dive into the research topics of 'Compact labeling schemes for ancestor queries'. Together they form a unique fingerprint.

Cite this