38.1 System Description

As the DAGS CD-ROM interface offers particularly powerful features for navigation and searching, concepts from this interface, in particular the random access feature allowing users to jump to a highlight within a speech have been integrated into the user interface for the DAGS'95 talks on the web.

At the core of the DAGS'95 proceedings is the talks user interface (fig. IV.13).

Figure IV.13 DAGS `95 Talks user interface

Each slide has a control panel above it containing clickable buttons and the title of the selected slide The slide title in the panel provides the user with an additional navigation cue. The "previous" and "next" buttons, represented by a left and a right arrow, allow the user to navigate sequentially through the talk without having to click on an item in the table of contents. The first audio clip available for downloading can be accessed via the leftmost sound icon on the control panel. Since the duration of the audio sample for each slide varies, the number of sound clips, i.e., the number of sound icons per slide also varies. In order to download the succeeding audio clips the user must click on each of the presented sound icons one after the other. The side-by-side view of the table of contents and the slide with the control panel above it is achieved by using <table> tags as specified in HTML 3.0 [Htm95]. Without using table tags it would not have been possible to reach a consistent layout of the slide screens on multiple platforms (Mac, Windows, UNIX).

Control panel design

To implement the control panel, we were initially planing on having a basic background while the button set and the text label would have been overlaid for each slide. This would have allowed for caching of the image resources such that moving to a different slide would not have required loading a new GIF file for the control panel. Unfortunately, we found that our ability to control detailed formatting information with HTML was too limited. Therefore we opted for a "one control panel per slide"-approach. This required to keep the control panel very small such that the download speed for new slides would only be marginally affected by also having to download the control panel for each slide.

Slide design

We first considered to convert text-only slides to HTML format, as this would have offered the best download performance. On slides with figures and other complicated graphics those would then have been inserted as smaller GIF files. We soon discovered that this approach would have prohibitively increased the complexity of creating WWW proceedings. We therefore decided to show all slides as images because this allowed us to retain the graphic quality of the overhead transparencies without additional editing.

Sound track

Presently, browsers use various helper applications to present non-text-data like sound or movies. A common format for voice or talk audio files for all platforms using WWW browsers is 8 bit, 8 MHz, AU format. Since there is currently no general standard for audio compression on all three target platforms, we decided to store the files in uncompressed AU format.

Each page of the talks also includes a link from the header of the page to the main entry point of the DAGS'95 proceedings as well as a link to the speaker's home page or, if no such page is available, to a page containing a summary of the speaker's profiles.