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Authoring and Design for the WWW

Appendix Three: Adobe Acrobat

General character

Acrobat was designed to serve two purposes:

Acrobat puts emphasis on the appearance of the page and in doing so takes the fixed formatting approach. It contrasts strongly with HTML which emphasises the structural components of the content, and which is currently not capable of specifying exactly how the page should look.

We can compare Acrobat's approach to the four problems in interactive electronic publishing which we identified in discussing HTML.

Proprietary hardware and software formats

Adobe's PDF file format is open and published, but not an agreed standard. Its design represents Adobe's view of what should be possible. However, we should recall that Postscript, without which high-quality desktop publishing might not have been achieved, was (and still is) an Adobe proprietary format. PDF files must be read with the Acrobat reader, which can be distributed free by the document publisher.

Fonts are property

Acrobat PDF documents can contain embedded definitions of the fonts needed. Property is protected in that the end-user cannot extract the fonts and use them in another document (Adobe are themselves major font publishers). Alternatively, when a document which does not contain embedded font information arrives at the user's machine, an approximation of the font is created on demand, using Adobe Multiple Master fonts.

Users constrained by hardware

Unlike HTML, Adobe documents have pages with actual dimensions, for example A4, and are in that sense virtual paper'. Rather than the document being fitted to the available space on the display, the user scrolls the document in the Acrobat viewer window (or sub-window within a Web browser). This scrolling can be avoided, at least for standard monitors, by designing pages which are the correct format for the screen but this approach, however desirable, clashes with the temptation to simply transfer wholesale to the screen existing documents designed for paper.

Documents self-contained, unconnected

Initially, PDF files could only link in hypertext fashion to other documents stored on the same server, and were therefore useless as components of distributed hypertext systems. However, the links embedded in PDF files can now be true URLs, allowing proper addressing of distant documents.

The PDF format is still extremely limited in its ability to create proper, maintainable hypertext links.

Features of the package

At its simplest, the user can 'print' a file to the PDF Writer (a virtual printer), which then makes a Portable Document Format file, which can be viewed on any platform for which an Acrobat Reader is available (Windows, Macintosh, DOS, Unix). The reader for Macintosh and Windows can be distributed free of charge. When the end-users open a document with the Reader, they can read it page by page, jump to any page, search for any word or phrase, and view the pages at a variety of degrees of magnification.

If the publisher wishes to provide a greater range of functions to the user, then they must use Acrobat Exchange. This application allows the authors to open a PDF file made with the PDF Writer and augment it in certain ways.

These include:

Other facilities in Acrobat Exchange include document security and facilities for deleting and adding pages, substituting pages, merging separate documents etc.

Using the package Acrobat Catalog authors can also create an index to enable faster searching by the end-user.

Some weaknesses of the Acrobat approach

The strengths of Acrobat are plain: the ease of production and the ability to guarantee what the end-user will see. Some of the weaknesses listed here may be avoided by future versions.

Poor facilities in the tool-set

None of the facilities for authors are automated to any useful extent within the Exchange package. Bookmarks can only be created manually one-by-one. Links must each be built by hand (whereas in HTML even the simplest word-processor could be used, say, to turn every occurrence of the word University' into a hypertext link to another document).

Other packages can produce PDF files directly, without resorting to the PDF writer, and in these cases, automation of certain functions is greatly improved. For example in Adobe PageMaker (Version 6) if a table of contents has been made for the publication, then, when a PDF file is made, this table can optionally be converted into the PDF bookmark list.

Document editing and maintenance

Hypertext links in PDF files are specified graphically, that is by their position on the page, not by the element such as a word or a picture which is to act as the trigger. At first site this seems unproblematic, since a strength of PDF is its ability to specify robustly exactly where items appear on each page. However, if we now imagine the creation and editing of a multipage document, the problems start to become apparent. If we create link hotspots (which we have to do by hand) on several pages, we have created a very fragile system, since if we edit the original and re- print' the PDF file, text flow has caused the text to shift away from under its hotspot, and this will be true for very hotspot on all the succeeding pages. This is exactly the danger we highlighted in discussing the weakness of fixed formatting approaches (p29).

Technically, this problem is not insoluble for future versions. However, using the current way in which Acrobat works, it effectively prevents the production of robust, maintainable documents.

Virtual paper?

In some respects, Acrobat's ease of transition from paper to screen-based documents can be seen as a problem rather than a virtue. It means that many documents will be produced which have been neither written nor designed for the screen. Parallel efforts by other manufacturers, for example the facility of the Microsoft Internet Explorer to directly display Microsoft Word and Excel documents without modification, should also be treated with care. It is important to distinguish between documents designed for on-screen interactive use and those pieces of virtual paper which are appropriately presented on screen as a representation of paper documents. Each medium has its strengths, and the Web will evolve its own genres with their own styles and modes of address, beyond the display of would-be paper.
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