Information distributed through the Web keeps growing faster day by day, and for this reason, several techniques for extracting Web data have been suggested during last years. Often, extraction tasks are performed through so called wrappers, procedures extracting information from Web pages, e.g. implementing logic-based techniques. Many fields of application today require a strong degree of robustness of wrappers, in order not to compromise assets of information or reliability of data extracted.
@cite_6 already suggested the possibility of exploiting previously acquired information, e.g. queries results, to re-induct a new wrapper from an old one not working anymore, because of structural changes in Web pages. @cite_9 compared results of simple tree matching and a modified weighed version of the same algorithm, in extracting information from HTML Web pages; this approach shares similarities to the one followed here to perform adaptation of wrappers. @cite_3 focused on robustness of wrappers exploiting absolute and relative XPath queries.
@cite_9 @cite_3 @cite_6
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The main issue for effective Web information extraction is how to recognize similar patterns in a Web page. Traditionally, it has been shown that pattern matching by using the HTML DOM tree is more efficient than the simple string matching approach. Nonetheless, previous tree-based pattern matching methods have problems by assuming that all HTML tags have the same values, assigning the same weight to each node in HTML trees. This paper proposes an enhanced tree matching algorithm that improves the tree edit distance method by considering the characteristics of HTML features. We assign different values to different HTML tree nodes according to their weights for displaying the corresponding data objects in the browser. Pattern matching of HTML patterns is done by obtaining the maximum mapping values of two HTML trees that are constructed with weighted node values from HTML data objects. Experiments are done over several Web commerce sites to evaluate the effectiveness of the proposed HTML tree matching algorithm. We demonstrate myPortal - an application for web content block extraction and aggregation. The research issues behind the tool are also explained, with an emphasis on robustness of web content extraction. During the last years, significant attention has been paid to the problem of building wrappers for extracting data from semistructured web sources. Nevertheless, since web sources are autonomous, they may experience changes that invalidate the wrappers. In this paper, we present new heuristics and algorithms to address the problem of automatic wrapper maintenance. Our approach is based on collecting query results during wrapper operation and using them later to generate new sets of examples that can be used to induce a new wrapper when the source changes.