Papers in PDF format

Pstohg — A Tool for Integrating Presentations into Hypermedia Systems
Jörn Bollmeyer
HEINZ NIXDORF INSTITUT
Universität-GH Paderborn, Fürstenallee 11, D-33102 Paderborn, Germany
email: bolle@uni-paderborn.de
Hypertext systems are becoming increasingly important in educational contexts where they are often used as
repositories for teaching material such as textbooks or other documents related to lectures [cf. Norman 1990].
On the other hand, the lectures themselves are often enhanced through the use of computer based
presentations, offering several advantages over „traditional“ technologies, such as overhead transparencies and
blackboards [cf. Lennon, Maurer 1994]. Since networked hypermedia systems like the WWW do not support
the creation of presentation material, specialized authoring tools like Microsoft´s Powerpoint are used.
However, the presented material needs to be accessible to the students after the lecture and should thus be
integrated into the same hypermedia system which stores any other documents related to the lecture. Apart
from writing a special viewer for each presentation program that is commonly used — an approach too costly
—, two degrees of integration may be distinguished.
1. Launching an external application: The presentation is stored in its native format; in order to access it, a
viewer for this data format needs to be available at the client side — like, e.g., the standalone viewer of
Powerpoint. The presentation may then be downloaded and the viewer started manually, or, more elegant
and easier to use, that viewer has been configured as an external viewer for a hypermedia system like
HyperWave.
2. Conversion into a supported data format: The presentation may be converted into some ,native" data
format that is supported by the hypermedia system. In this case, the Powerpoint slides have to be converted
into, e.g., a collection of image files in, say, GIF format. This type of integration is also used by tools that
convert animated presentations into Java applets.
The major advantage of the first approach is, that providing material is quite not very costly. On the other
hand, special viewers are needed on the student’s computer, that is on the client side. While these are often
available for free, they are also platform dependent: Powerpoint viewers, e.g., are not available for UNIX
systems. Another important problem using external viewers is the fact, that the presentation can make no use
of the functionality of the hypermedia system: no links into the hypermedia base or from those documents into
some specific point within the presentation may be defined.
With the second solution, the preparation of a slide show accessible from the hypermedia system becomes more
costly as long as there are no appropriate tools. However, the advantages more than compensate the additional
effort. Hyperlinks may be defined from any arbitrary slide, even from specified points within a slide, to any
other hypermedia document within the system, that is any other HyperWave or WWW document, and vice
versa. Also, the slides may be viewed on any platform — as long as a web viewer exists supporting the chosen
data format.
Because of its obvious advantages, we decided to follow the second approach. A tool has been developed that
converts PostScript files with minimal DSC information slide by slide into a sequence of GIF images, linking
them by default in a linear fashion. It is thus only necessary to „print“ the presentation into a PostScript file.
With HyperWave, this file might be stored directly — with slow rendering and at the expense of losing all
colour information —, whereas with most other WWW services PostScript is only supported by an external
viewer; we would thus be ending up in case 1 above. Our tool then uses the HyperWave Interchange Format to
create a collection at a specified location on a HyperWave server — supporting a number of options such as
resolution, clipping or orientation. The presentation is then ready to use; additional links to and from other
hypermedia documents may be added to any of the slides, since GIF is a fully supported HyperWave format.
The same method also works with standard WWW clients, where the use of image maps, or a Java aequivalent,
is needed for true hypermedia functionality. We have thus found a method for a seamless and simple