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Dissertation Information for Abdullah Al-Shehri

NAME:
- Abdullah Al-Shehri

DEGREE:
- Ph.D.

DISCIPLINE:
- Library and Information Science

SCHOOL:
- University of Pittsburgh (USA) (2001)

ADVISORS:
- None

COMMITTEE MEMBERS:
- Edie Rasmussen

MPACT Status: Incomplete - Not_Inspected

Title: Organization and effectiveness of n-gram approach for indexing and retrieval in Arabic information retrieval systems

Abstract: This dissertation explores a valid alternative to the word method for indexing and retrieving Arabic documents based on a finite number of word fragments, called n-grams. Based on the statistical properties of n-grams in six Arabic corpora, an optimization function of the size of n-grams is developed in terms of entropy and computational cost of n-grams. Two n-gram-based methods for indexing and retrieving Arabic documents are developed: optimal n-grams and extended optimal n-grams. The former uses optimal size of n-grams and the latter eliminates noisy optimal n-grams and expands them to a higher order of n-grams. An experimental Arabic 1RS was designed to conduct several retrieval experiments on two Arabic document collections: the SACS and the Al-Raya. The retrieval results of the n-gram-based methods are contrasted and compared to the word method in terms of precision-recall scores. In addition, the study investigates the effects of centroid vectors on the retrieval effectiveness of the word-based indexing method and the n-gram-based indexing methods.

The dissertation concludes that the percentage of the actual occurrences of unique overlapping n-grams to the expected occurrences decreases sharply as the size of n increases. The overlapping n-grams are not distributed with equal probability but in a highly skewed fashion. The optimal n-grams are defined as 3-grams and the extended optimal n-grams are defined as e-3-5-grams. The retrieval and statistical tests results show that the 3-grams retrieval method illustrates its superiority over the word retrieval method and the e3-5-grams retrieval method on the SACS collection but it has problems with the number of irrelative documents retrieved. On the Al-Raya collection, both the 3-grams and e-3-5-grams retrieval methods provide similar retrieval effectiveness but the advantage of the latter is it retrieves few irrelevant documents. The centroid vectors of words, 3-grams, and e-3-5-grams reduce the retrieval effectiveness on the SACS collection and maintain the retrieval effectiveness and reduce the average number of retrieved documents on the Al-Raya collection.

MPACT Scores for Abdullah Al-Shehri

A = 0
C = 0
A+C = 0
T = 0
G = 0
W = 0
TD = 0
TA = 0
calculated 2008-01-31 06:33:36

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Students under Abdullah Al-Shehri

ADVISEES:
- None

COMMITTEESHIPS:
- None