Multiple-device authoring

Web Page Filtering and Re-Authoring for Mobile Users

timothy bickmore,andreas girgensohn and joseph W. sullivan

The Digestor system automatically converts web-based documents designed for desktop viewing into formats appropriate for handheld devices with small display screens, such as Palm-PCs, PDAs, and cellular phones. Digestor employs a heuristic planning algorithm and a set of structural page transformations to produce the 'best' looking document for a given display size. Digestor can also be instructed, via a scripting language, to render portions of documents, thereby avoiding navigation through many screens of information. Two versions of Digestor have been deployed, one that re-authors HTML into HTML for conventional browsers and one that converts HTML into HDML for Phone.com's micro-browsers. Digestor provides a crucial technology for rapidly accessing, scanning and processing information from arbitrary web-based documents from any location reachable by wired or unwired communication.

INTRODUCTION

Several research projects have demonstrated access to world-wide web (WWW) documents from personal electronic devices. Now such access is a commercial reality. Personal digital assistants (PDAs) with networking functionality now come packaged with web browsers, and web-like browsers are commercially available for cellular phones and two-way pagers.

Unfortunately for the mobile users, most web documents are designed for display on desktop computers with color monitors having at least 640 x 480 resolution and many documents are designed with resolutions of 1024 x 768 and larger in mind. This leads to a ratio from four- to 100-to-one of designed available screen area, making direct presentation of documents on small devices aesthetically unpleasant, un-navigable and, in the worst case, completely undecipherable. This presents the central problem addressed in our work: how to display arbitrary HTML documents that have been designed for desktop systems on personal electronic devices that have more limited input/output (I/O) capabilities?

In the larger context of mobile and ubiquitous computing, Digestor provides a key technology for giving users view-mobility over platforms [5]. Today, technologies already provide computational mobility and wireless connectivity, but the standard solutions to viewing documents and web pages on tiny screens are to either increase the screen resolution, which is great if you carry a magnifying glass with you or to provide the ability to fax or print to a local hardcopy device, which is both inconvenient and contradicts the rationale for having electronic documents in the first place. Digestor performs an automatic re-authoring of web documents to make them fit on small displays.

PREVIOUS WORK

We have categorized techniques for displaying WWW pages on small screen devices into five general approaches: device-specific authoring, multiple-device authoring, client-side navigation, automatic re-authoring, and web page filtering. This section describes these approaches and analyzes their advantages and disadvantages.

Device-specific authoring

Device-specific authoring involves authoring a set of WWW pages for a particular display device, for example a cellular phone fitted with a display and communications software such as the Nokia 9000. The basic philosophy in this approach is that users of such specialty devices will only have access to a select set of services, and the pages for these services can all be designed up-front for the device's particular display. Information may be provided from the WWW at large, but the desired pages must be pre-defined and custom information extraction and page formatting software must be written to deliver the information to the small device. This is the approach taken in Phone.com's (formerly Unwired Planet) UP.Link service [6] that uses a proprietary mark-up language (HDML).

Multiple-device authoring

In multiple-device authoring, a range of target devices are identified and mappings from a single source document to a set of rendered documents are defined to cover the devices within the range. One example of this is the StretchText approach [7], in which portions of the document (potentially down to the word level) can be tagged with a 'level of abstraction' measure. Upon receiving the document, users can specify the level of abstraction they wish to view and are presented with the corresponding detail. Another example of multiple-device authoring is HTML cascading style sheets (CSS) [8]. In CSS, a single style sheet defines a set of display attributes for different structural portions of a document (e.g. all top-level section headings are to be displayed in red 18-point Times font). A series of style sheets may be attached to a document, each with a weight describing its desirability to the document's author. The user can also specify a style sheet, as can the WWW browser using the 'default' style sheet. Although the author's style sheets normally override the user's, the user can selectively enable or disable the author's, providing them with the ability to tailor the rendering of the document to their particular display.