NDLI: Partial-Match Retrieval Algorithms

Content Provider	Society for Industrial and Applied Mathematics (SIAM)
Author	Rivest, Ronald L.
Copyright Year	1976
Abstract	We examine the efficiency of hash-coding and tree-search algorithms for retrieving from a file of k-letter words all words which match a partially-specified input query word (for example, retrieving all six-letter English words of the form S*RH where * is a dont care character).We precisely characterize those balanced hash-coding algorithms with minimum average number of lists examined. Use of the first few letters of each word as a list index is shown to be one such optimal algorithm. A new class of combinatorial designs (called associative block designs) provides better hash functions with a greatly reduced worst-case number of lists examined, yet with optimal average behavior maintained. Another efficient variant involves storing each word in several lists.Tree-search algorithms are shown to be approximately as efficient as hash-coding algorithms, on the average.In general, these algorithms require time about $O(n^{(k - s)/k} )$ to respond to a query word with s letters specified, given a file of nk-letter words. Previous algorithms either required time $O(s \cdot n/k)$ or else used exorbitant amounts of storage.
Starting Page	19
Ending Page	50
Page Count	32
File Format	PDF
ISSN	00975397
DOI	10.1137/0205003
e-ISSN	10957111
Journal	SIAM Journal on Computing (SMJCAT)
Issue Number	1
Volume Number	5
Language	English
Publisher	Society for Industrial and Applied Mathematics
Publisher Date	1976-03-01
Access Restriction	Subscribed
Subject Keyword	hash-coding associative retrieval analysis of algorithms partial-match retrieval searching tree-search
Content Type	Text
Resource Type	Article
Subject	Mathematics Computer Science

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