[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Structured from/within unstructured documents
On Sun, 16 Dec 2007 18:15:05 +1100, Greg Hunt wrote > Stephen, > The problem with processing the physical PDF file is precisely its presentation orientation. You have to render PDF (at least internally into a buffer). Its a format with graphical "language" not totally unlike (and built-upon) PostScript where, among a host of features, each individual character can be positioned. Popular "freely" available PDF tools that can be used to "extract text" are, among others, Adobe's Acrobat Reader, Derek Noonburg's Xpdf, Poppler and Ghostscript. M$ Windows includes a "filter mechanism" called iFilter for their own search. It includes apparently, among others, a filter supplied by Adobe intended for the extraction of text from PDF. > A perverse document can mix image and text or even embed the text in the reverse order that it would be displayed in. Not really that wholly uncommon--- calculating glymph position from the right. > In rendering, however, you need or want to keep paragraph blocks together and **not** (as the case from a "screen scrape" of a display rendered page) preserve the columns and visual flow elements as these not only make it much more difficult to extract simple things like sentences but also don't deliver any contextual information. That a text was set in two column with a center picture is a result of its chosen style and not content structure--- recall that different output devices can look different. Linking structural semantics for many of these style elements is tenuous. -- Edward C. Zimmermann, Basis Systeme netzwerk, Munich Office Leo (R&D): Leopoldstrasse 53-55, D-80802 Munich, Federal Republic of Germany http://www.nonmonotonic.net
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