XWRAP: An XML-Enabled Wrapper Construction System for Web Information Sources

The amount of useful semi-structured data on the web continues to grow at a stunning pace. Often interesting web data are not in database systems but in HTML pages, XML pages, or text les. Data in these formats is not directly usable by standard SQL-like query processing engines that support sophisticated querying and reporting beyond keyword-based retrieval. Hence, the web users or applications need a smart way of extracting data from these web sources. One of the popular approaches is to write wrappers around the sources, either manually or with software assistance, to bring the web data within the reach of more sophisticated query tools and general mediator-based information integration systems. In this paper, we describe the methodology and the software development of an XML-enabled wrapper construction system XWRAP for semi-automatic generation of wrapper programs. By XML-enabled we mean that the metadata about information content that are implicit in the original web pages will be extracted and encoded explicitly as XML tags in the wrapped documents. In addition, the query-based content ltering process is performed against the XML documents. The XWRAP wrapper generation framework has three distinct features. First, it explicitly separates tasks of building wrappers that are speci c to a Web source from the tasks that are repetitive for any source, and uses a component library to provide basic building blocks for wrapper programs. Second, it provides inductive learning algorithms that derive or discover wrapper patterns by reasoning about sample pages or sample speci cations. Third and most importantly, we introduce and develop a twophase code generation framework. The rst phase utilizes an interactive interface facility to encode the source-speci c metadata knowledge identi ed by individual wrapper developers as declarative information extraction rules. The second phase combines the information extraction rules generated at the rst phase with the XWRAP component library to construct an executable wrapper program for the given web source. The two-phase code generation approach exhibits a number of advantages over existing approaches. First, it provides a user-friendly interface program to allow users to generate their information extraction rules with a few mouse clicks. Second, it provides a clean separation of the information extraction semantics from the generation of procedural wrapper programs (e.g., Java code). Such separation allows new extraction rules to be incorporated into a wrapper program incrementally. Third, it facilitates the use of the micro-feedback approach to revisit and tune the wrapper programs at run time. We report the performance of XWRAP and our experiments by demonstrating the bene t of building wrappers for a number of Web sources in di erent domains using the XWRAP generation system. This research is partially supported by DARPA contract MDA972-97-1-0016 and a grant from Intel.