A Compact In-Memory Dictionary for RDF data

Hamid R. Bazoubandi, Steven de Rooij, Jacopo Urbani, Annette ten Teije, Frank van Harmelen, Henri Bal

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


While almost all dictionary compression techniques focus on static RDF data, we present a compact in-memory RDF dictionary for dynamic and streaming data. To do so, we analysed the structure of terms in real-world datasets and observed a high degree of common prefixes. We studied the applicability of Trie data structures on RDF data to reduce the memory occupied by common prefixes and discovered that all existing Trie implementations lead to either poor performance, or an excessive memory wastage. In our approach, we address the existing limitations of Tries for RDF data, and propose a new variant of Trie which contains some optimizations explicitly designed to improve the performance on RDF data. Furthermore, we show how we use this Trie as an in-memory dictionary by using as numerical ID a memory address instead of an integer counter. This design removes the need for an additional decoding data structure, and further reduces the occupied memory. An empirical analysis on realworld datasets shows that with a reasonable overhead our technique uses 50–59% less memory than a conventional uncompressed dictionary.
Original languageEnglish
Title of host publicationThe Semantic Web: Latest Advances and New Domains - 12th European Semantic Web Conference, ESWC 2015, Proceedings
Number of pages16
ISBN (Electronic)9783319188171
Publication statusPublished - 2015
Event12th European Semantic Web Conference (ESWC 2015) - Portoroz, Slovenia
Duration: 31 May 20154 Jun 2015

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349


Conference12th European Semantic Web Conference (ESWC 2015)

Bibliographical note

Proceedings title: Proceedings of the twelfth European Semantic Web Conference
Publisher: Springer
Place of publication: Berlin


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