Adaptive Comparison-Based Algorithms for Evaluating Set Queries

Computer Science;Adaptive algorithm;comparison-based algorithm;search engines;algorithms

Mirzazadeh, Mehdi

University of Waterloo

关键词: Computer Science;    Adaptive algorithm;    comparison-based algorithm;    search engines;    algorithms;   

Others  :  https://uwspace.uwaterloo.ca/bitstream/10012/1147/1/mmirzaza2004.pdf

瑞士|英语

来源: UWSPACE Waterloo Institutional Repository

【 摘 要 】

In this thesis we study a problem that arises in answering boolean queries submitted to a search engine. Usually a search engine stores the set of IDs of documents containing each word in a pre-computed sorted order and to evaluate a query like ;;computer AND science;; the search engine has to evaluate the union of the sets of documents containing the words ;;computer;; and ;;science;;. More complex queries will result in more complex set expressions. In this thesiswe consider the problem of evaluation of a set expression with union and intersection as operators and ordered sets as operands. We explore properties of comparison-based algorithms for theproblem. A proof of a set expression is the set of comparisons that a comparison-based algorithm performs before it can determine the result of the expression. We discuss the properties of the proofs of set expressions and based on how complex the smallest proofs of a set expression E are, we define a measurement for determining how difficult it is for E to be computed. Then, we design an algorithm that is adaptive to the difficulty of the inputexpression and we show that the running time of the algorithm is roughly proportional to difficulty of the input expression, where the factor is roughly logarithmic in the number of the operands of the input expression.