Degree Name

Doctor of Philosophy


Faculty of Informatics


Given the phenomenal rate by which the World Wide Web is changing, retrieval methods and quality assurance have become bottleneck issues for many information retrieval services on the Internet, e.g. Web search engine designs. In this thesis, approaches that increase the efficiency of information retrieval methods, and provide for quality assurance of information obtained from the Web, are developed through the implementation of a quality-focused information retrieval system. A novel approach to the retrieval of quality information from the Internet is introduced. Implemented as a component of a vertical search application, this results in a focused crawler which is capable of retrieving quality information from the Internet. The three main contributions of this research are: (1) An effective and flexible crawling application that is well-suited for information retrieving tasks on the dynamic World Wide Web (WWW) is implemented. The resulting crawling application (crawler) is designed after having observed the dynamics of the web evolution through regular monitoring of the WWW; it also addresses the shortcomings of some existing crawlers, therefore presenting itself as a practical implementation. (2) A mechanism that converts human quality judgement through user surveys into an algorithm is developed, so that user perceptions of a set of criteria which may lead to determination of the quality content on the web page concerned, can be applied to a large amount of Web documents with minimal manual effort. This was obtained through a relatively large user survey which was conducted in a collaborative research work with Dr Shirlee-Ann Knight of Edith Cowan University. The survey was conducted to determine what criteria Web documents are perceived to meet to qualify as a quality document. This results in an aggregate numeric score for each web page between 0 and 1 respectively indicating that it does not meet any quality criteria, or that it meets all quality criteria perfectly. (3) This research proposes an approach to predict the quality of a web page before it is retrieved by a crawler. The approach allows its incorporation into a vertical search application which focuses on the retrieval of quality information. Experimental results on real world data show that the proposed approach is more effective than any other brute force approaches which have been published so far. The proposed methods produce a numerical quality score for any text based Web document. This thesis will show that such score can also be used as a web page ranking criterion for horizontal search engines. As part of this research project, this ranking scheme has been implemented and embedded into a working search engine. The observed user feedback confirms that search results when ranked by quality score, satisfy user needs more satisfactorily than when ranked by other popular ranking schemes such as PageRank or relevancy ranking. It is also investigated whether the combination of quality score with existing ranking schemes can further enhance the user experience with search engines.

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