On safety, computability and local property of web queries

Authors:
Hong-Cheu Liu;Jeffrey Xu Yu
Affiliations:
Department of Computer Science and Information Engineering, Diwan University, Madou, Tainan County, Taiwan;Department of System Engineering and Engineering Management, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong
Venue:
APWeb'08 Proceedings of the 10th Asia-Pacific web conference on Progress in WWW research and development
Year:
2008

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Abstract

In this paper, we study the safety of formulas, computability and local property of Web queries. The limited access capability and loosely structured information make querying the Web significantly different from querying a conventional database. When evaluating queries on the Web, it is not feasible to exhaustively examine all objects on the Web. The local property, studied in this paper, can be informally described as the reverse scenario: in order to check if an object participated in the result of a Web query, is it sufficient to examine a bounded portion of the Web? We start our investigation by using the Web machine proposed by Mendelzon and Milo [1]. We review the genericity, domain independence and computability of Web queries. We present a syntactic class of local Web queries and a sound algorithm to check if a query belongs to this class. We then examine the notion of locality of two popular XML query languages, namely XPath and XQuery, and show that they are not local.