W3-Access for Blind People
Louis Perrochon, Andrea Kennel,
Institut für Informationssysteme,
ETH Zürich,
Switzerland.
louis@perrochon.com, kennel@inf.ethz.ch
Introduction
Blind users cannot use a state-of-the art mouse because a mouse
normally requires visual feedback from the screen to the user. As a
consequence, when working with hypertexts, blind users cannot simply
click on a magic blue word in the middle of the screen. Normally they
have to search for it word by word using a screen reader.Another
general problem is that blind users cannot get an overview of the
structure of a text with one quick glance at the screen. Thus blind
users can be "lost in hyperspace" very quick. Of course the correct
solution is building better screen readers. However this is not that
easy. We present a simple solution that solves some of these problems
for W3-access. Our approach works with every W3-browser
on every system. No additional software has to be installed at the
user's computer.
Architecture
We insert a transformer between the W3-browser and the W3-server. The
transformer modifies each document to reflect its structure
clearer.
Figure 1. Architecture of 'W3-Access for Blind People'
The Information-Provider's View
No changes have to be made to HTML documents or W3 servers.
The User's View
The user knows nothing about proxies and what they do. He only sees
the modified documents.
General Structure of Documents
When the user loads a hypertext via our proxy server, he will get a
modified version of the requested document. The modified document has
three parts: (1)The requested document, with some modifications, (2) a
list of all the links in the document and (3) a nested list of all the
titles. The two lists give an overview over the document and allow
the user to navigate easily through it. Throughout the modified
document, new links are introduced.
The List of Links
The very first reference at the top of each modified document is a
reference to the list of links at the end of the modified document.
After activation of this reference, the beginning of the list of links
will appear at the top of the browser window. The first entry of the
list of links indicates the number of links in the list. The following
entries in the list are copies of all the links in the original
document. The very last entry in the list points back to the top of
the modified document.
The List of Titles
Most hypertexts have a hierarchical title structure: titles of level
one (<H1>) contain several titles of level two
(<h2>) which contain subtitles of level three
(<h3>) and so on. In a hypertext, the blind user can
get a quick overview just by browsing through the titles of level one
(<H1>). Thus a nested list of all the titles is added to
the original document. Additionally, the entries in the list of titles
are references to the titles in the text. Thus interesting titles in
the text can immediately be found. Another possibility is to go down
the title hierarchy and find all subtitles of this title.
The Proxy-Provider's View
Anybody can use the proxy server running at ETH Zurich. However, it
might be wise to set up more proxies. They will reduce network
traffic, as everybody can access the nearest proxy.
The proxy-server is a modified CERN-httpd-daemon. The provider has to
add one line to the proxy code and change one line in the makefile. Of
course some files of ours have to be added to the files of the
distribution, too. After compilation, the httpd is started in
proxy-only mode.
Our proxy-server is configurable. There are two files, that control
the transformation process. One is used to define all the keywords,
that are inserted into the HTML documents in front of special HTML
elements, the other defines the transformation of each HTML
element. See the documentation for more details on how to configure
the proxy.
Extended abstract. More documentation and our code is freely
available at http://www.inf.ethz.ch/department/IS/ea/blinds/.
To try it yourself, set your proxy to
http://ea.ethz.ch:8080/, flush your cache and start
browsing.