document: Efficient web change monitoring with page digest The Internet and the World Wide Web have enabled a publishing explosion of useful online information , which has produced the unfortunate side effect of information overload : it is increasingly difficult for individuals to keep abreast of fresh information . In this paper we describe an approach for building a system for efficiently monitoring changes to Web documents . This paper has three main contributions . First , we present a coherent framework that captures different characteristics of Web documents . The system uses the Page Digest encoding to provide a comprehensive monitoring system for content , structure , and other interesting properties of Web documents . Second , the Page Digest encoding enables improved performance for individual page monitors through mechanisms such as short-circuit evaluation , linear time algorithms for document and structure similarity , and data size reduction . Finally , we develop a collection of sentinel grouping techniques based on the Page Digest encoding to reduce redundant processing in large-scale monitoring systems by grouping similar monitoring requests together . We examine how effective these techniques are over a wide range of parameters and have seen an order of magnitude speed up over existing Web-based information monitoring systems .
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