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different search engines but that require solutions specifically tailored for data-driven diagrams.

Diagram Corpus Extraction

Obtaining the text of a Web document is usually as easy as downloading and parsing an HTML file; in contrast, statistical diagrams require special processing to extract useful information. They are embedded in PDFs with little to distinguish them from surrounding text, the text embedded in a diagram is highly stylized with meaning that is very sensitive to the text’s precise role, and, because diagrams are often an integral part of a highly engineered document, they can have extensive “implicit hyperlinks” in the form of figure references from the body of the surrounding text. Our Diagram Extractor component attempts to recover all of the relevant text for a diagram and determine an appropriate semantic label (caption, y-axis label, etc.) for each string.

Ranking Quality

All search engines must figure out how to score an object’s relevance to a search query, but scoring diagrams for relevance can yield strange and surprising results. We use the metadata extracted from the previous step to obtain search quality that is substantially better than naive methods.

Snippet Generation

Small summaries of the searched-for content, usually called snippets, allow users to quickly scan a large number of results before actually selecting one. Conventional search engines select regions of text from the original documents, while image search engines generally scale down the original image to a small thumbnail. Neither technique can be directly applied to data-driven diagrams. Obviously, textual techniques will not capture any visual elements. Figure 1 shows that image scaling is also ineffective: although photos and images remain legible at smaller sizes, diagrams quickly become difficult to understand.

This paper describes DiagramFlyer, a search engine for finding data-driven diagrams in Web documents. It addresses each of the above challenges, yielding a search engine that successfully extracts diagram metadata in order to provide both higher-quality ranking and improved diagram “snippets” for fast search result scanning.

The techniques we propose are general and can work across diagrams found throughout the Web. However, in our current testbed we concentrate on diagrams extracted from PDFs that were discovered and downloaded from public Web pages on academic Internet domains. Our resulting corpus contains 153,000 PDFs and 319,000 diagrams. We show that DiagramFlyer obtains a 52% improvement in

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