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Author Navarro, Gonzalo
Source ACM Digital Library
Content type Text
Publisher Association for Computing Machinery (ACM)
File Format PDF
Copyright Year ©2009
Language English
Subject Domain (in DDC) Computer science, information & general works ♦ Computer programming, programs & data
Subject Keyword Data structures ♦ Coding and information theory ♦ Data storage representations ♦ Indexing methods ♦ Textual databases
Abstract The LZ-index is a theoretical proposal of a lightweight data structure for text indexing, based on the Ziv-Lempel trie. If a text of $\textit{u}$ characters over an alphabet of size σ is compressible to $\textit{n}$ symbols using the LZ78 algorithm, then the LZ-index takes $4\textit{n}$ $log_{2}$ $\textit{n}$ $(1+\textit{o}(1))$ bits of space (that is, 4 times the entropy of the text) and reports the $\textit{R}$ occurrences of a pattern of length m in worst case time $O(m^{3}$ log σ + $(\textit{m}$ + $\textit{R})log$ $\textit{n}).$ In this paper we face the challenge of obtaining a practical implementation of the LZ-index, which is not at all straightforward from the theoretical proposal. We end up with a prototype that takes the promised space and has average search time $\textit{O}(σ$ $\textit{m}$ log $\textit{u}$ + $&sqrt;\textit{uR}).$ This prototype is shown to be faster than other competing approaches when we take into account the time to report the positions or text contexts of the occurrences found. We show in detail the process of implementing the index, which involves interesting lessons of theory versus practice.
ISSN 10846654
Age Range 18 to 22 years ♦ above 22 year
Educational Use Research
Education Level UG and PG
Learning Resource Type Article
Publisher Date 2009-02-01
Publisher Place New York
e-ISSN 10846654
Journal Journal of Experimental Algorithmics (JEA)
Volume Number 13
Page Count 48
Starting Page 1.2
Ending Page 1.49


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Source: ACM Digital Library