Data integrity constraints are fundamental in various applications, such as data management, integration, cleaning, and schema extraction. This paper presents the results of a first comprehensive study on finding inclusion dependencies on the Web. The problem is important because (1) applications of inclusion dependencies, such as data quality management, are beneficial in the Web context, and (2) such dependencies are not explicitly given in general. In our approach, we enumerate pairs of HTML/XML elements that possibly represent inclusion dependencies and then rank the results for verification. First, we propose a bit-based signature scheme to efficiently select candidates (element pairs) in the enumeration process. The signature scheme is unique in that it supports Jaccard containment to deal with the incomplete nature of data on the Web, and preserves the semiorder inclusion relationship among sets of words. Second, we propose a ranking scheme to support a user in checking whether each enumerated pair actually suggests inclusion dependencies. The ranking scheme sorts the enumerated pairs so that we can examine a small number of pairs for simultaneously verifying many pairs. Finally, we prove that there exist efficient algorithms for the ranking scheme. In addition to the theoretical results for the signature and ranking schemes, we present a comprehensive set of experimental results using various real Web sites. The results show that in the enumeration process the signature scheme reduces the number of candidate pairs by orders of magnitude, and that the ranking scheme allows a small number of higher ranked results to cover many other pairs.2

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