Personalizable edge services for Web accessibility.

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Personalizable Edge Services for Web Accessibility
Gennaro Iaccarino
ISISLab
Dipartimento di Informatica ed
Applicazioni “R.M. Capocelli”
Universit` a di Salerno, Italy
iaccar@dia.unisa.it
Delfina Malandrino
ISISLab
Dipartimento di Informatica ed
Applicazioni “R.M. Capocelli”
Universit` a di Salerno, Italy
delmal@dia.unisa.it
Vittorio Scarano
ISISLab
Dipartimento di Informatica ed
Applicazioni “R.M. Capocelli”
Universit` a di Salerno, Italy
vitsca@dia.unisa.it
ABSTRACT
Web Content Accessibility guidelines by W3C [29] provide sev-
eral suggestions for Web designers on how to author Web pages
in order to make them accessible to everyone. In this context, we
are proposing the use of edge services as an efficient and general
solution to promote accessibility and breaking down the digital bar-
riers that inhibit users with disabilities to actively participate to any
aspect of our society.
To this aim, we present in this paper PAN: Personalizable Acces-
sible Navigation, that is a set of edge services designed to improve
Web pages accessibility, developed and deployed on top of a pro-
grammable intermediary framework [8].
The characteristics and the location of the services, i.e. provided
by intermediaries, as well as the personalization and the opportu-
nities to select multiple profiles make PAN a platform that is espe-
cially suitable in accessing the Web seamlessly also from mobile
terminals.
Categories and Subject Descriptors
H.4 [Information Systems Applications]; H.5 [Information In-
terfaces and Presentation]; K.4 [Computers and Society]: So-
cial issues—Handicapped persons/special needs
General Terms
Human Factors
Keywords
Web Accessibility, Programmable edge servers, disability, univer-
sal access.
1.INTRODUCTION
The World Wide Web, with its ability to is a “24x7 source of in-
formation”, and the services it provides, is a remarkable reality in
our society. Many different explanations can motivate this aston-
ishing success, from technological to sociological to economical
ones. Among the former, very important is the emphasis on the
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capabilities of the standards to accommodate a wide range of ser-
vices, therefore, pushing the World Wide Web as a universal access
portal to the information, wherever located and however accessed.
In spite of this tremendous and strengthened success, an impor-
tant challenge affects the structure of the pages that the Web in-
creasingly provide every day: most of them are published without
any consideration about an important question: “is this Web page
accessible for everyone?”.
More specifically, Web accessibility means that people with dis-
abilities can easily navigate and interact with the Web. Conversely,
currently most Web sites have accessibility barriers that make dif-
ficult or impossible for many people with disabilities to use and ac-
cess the Web. Using keyboards and mouse, hearing video and audio
multimedia files, browsing through some intrusive Web pages (i.e.
Web pages with pop-ups, advertisements, etc.) could appear as a
normal activity for “non-disabled” people, but, on the other hand,
it appears as a not simple task for users with some type of disability.
Currently there are no universally accepted categorizations of
disability, but as described in [10] they can be classified into the
following main categories: Visual disabilities, that include blind-
ness (uncorrectable loss of vision) low vision and color blindness
(a lack of sensitivity to certain colors); Hearing Impairments that
include deafness (uncorrectable impairment of hearing) or a mild
hearing impairment; Physical disabilities that include motor dis-
abilities (weakness, limitations of muscular control, such as lack of
coordination, limitations of sensation in hands and arms); Speech
disabilities that include difficulty in producing speech that is rec-
ognizable by software for voice recognition; Cognitive disabilities
that include, for example, dyslexia, attention deficit disorder, intel-
lectual and memory impairments.
In particular, in the above classification, visual impairments pro-
duce the most common source of difficulty for users accessing the
Web. Small fonts, some text and background color combinations,
background images, and blinking text represent a problem for Web
users. Moreover, blind people notice several problems ifWebpages
are composed of a lot of images, tables, and not only of linear text.
In addition, for users with hearing impairments, the most critical
difficulty comes from the increasing popularity of audio and video
multimedia applications that, on the other hand, represent an in-
creasingly important part of many Web sites today.
Of course, the accessibility problems are greatly enhanced by the
navigation by mobile terminals, since the “traditional” transcoding
operates only taking into account the limitations of the devices and
not taking into account the potential disabilities of the user. In lit-
erature, we can find several examples of intermediary adaptation
systems for mobile terminals such as iMobile by AT&T [25], the

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TACC infrastructure [11], RabbIT1and Privoxy2.
Our goal. In this paper we present PAN: Personalizable Acces-
sible Navigation, that is, a set of edge services that aims to make
the navigation on the Web more accessible for any user that access
it. In particular, our main goal is to provide efficient adaptation
services, that is, services that are able to apply different type of
on-the-fly transformations on Web pages, in order to meet different
users preferences/needs/abilities.
The rationale that lead our project is the effectiveness of inter-
mediary frameworks to efficiently provide services in a transparent
way for end users that, therefore, could benefit of complex func-
tionalities anytime, anywhere and by using any client device. Users
with disabilities can take advantage of the provided edge services
by simply choosing a profile, among the provided ones (or to define
a new profile from scratch), that mainly suit their needs. Finally, it
must be emphasized that improvements on Web pages could posi-
tively affect all users, for example, support for speech output could
not only benefits blind users, but also Web users whose eyes are
busy with other tasks.
Organizationofthepaper. In the next section, we present the
important issue of Web accessibility and, therefore, strongly moti-
vate our research. Moreover, we present some examples of acces-
sibility systems that exist in literature, and some example of inter-
mediary frameworks that could be programmed to provide accessi-
bility services. In particular, we first describe how programmable
proxies can be employed to promote accessibility, and in general,
tackle a relevant part of the problems that are generated by the dy-
namic nature of the Web, then, we briefly we introduce the plat-
forms for programmable HTTP proxies that are available nowa-
days. In Section 3 we provide some details about PAN and its
configuration and the multiple profiles options. In Section 4 we
present PAN’s services that can be used for efficiently providing
accessibility to people for disabilities, in several contexts, included
the mobile Web. Finally, in Section 5, we conclude with some final
comments.
2.WEB ACCESSIBILITY
The W3C Consortium is employing a lot of efforts and is leading
a lot of activities to make the most famous information space acces-
sible for anyone, and then allow people with disabilities to actively
perceive, understand, navigate, and interact with the Web.
Within this area our interest is mainly devoted to the provision
of personalized applications, that is, applications that are able to
customize Web content according to users’ preferences and needs.
In particular we have implemented some examples of services that
make Web pages more accessible for users with visual and motor
disabilities.
Some disabilities, such as hearing impairments, do not require
any transformation on HTML pages accessed by users. Visual and
motor impairments could be addressed by using screen readers or
assistive technologies, respectively (modified keyboards or soft-
ware for keyboard and mouse emulation). But our aim is how to
address these challenges with an instrument that is able to person-
alize the Web without any modification both on client and server
systems.
Some surveys3on accessibility in Web design estimate that there
are 180 million people worldwide who are visually impaired, 45
1http://rabbit-proxy.sourceforge.net
2http://www.privoxy.org
3http://www.lighthouse.org/
million are blind and 135 million are partially sighted. In the US,
16.5 million people suffer of vision impairments. Finally, the ef-
forts in making the Web a more accessible place is very important
since the the rapid aging of the population and the estimated in-
crease of disabled users (a reasonable estimate is a doubling by
2020 worldwide and a total of 20 million US people by 2010).
2.1Examples of Web accessibility systems
Assistive devices, like screen readers and audio browsers, are be-
ing used by blind users to access the Web. However, these systems
show limitations since they are not able to filter Web pages for re-
moving useless information involving users, bothered by more and
more intrusive elements, to quickly leave their frustrating naviga-
tion.
In order to address this issue, several systems have been devel-
oped with the aim at providing Web content accessible to everyone.
These systems, that can be classified as filter and transformation
tools, include for example, systems that build an only-text version
of Web documents (BETSIE and textualise), systems that apply
transformation according to users’ preferences (Web Access Gate-
way and Tablin), systems that apply transformations according to
specific rules and heuristics (WAB).
BETSIE, acronym of BBC Education Text to Speech Internet
Enhancer [6], is a simple CGI Perl script whose main goal is to
tackle the difficulties experienced by people using text-to-speech
systems for Web browsing. BETSIE produces on-the-fly text-only
version of every Web page navigated by the end user and, in par-
ticular, it modifies Web pages by handling frames, by linearizing
tables, by removing images, Java and Javascript code, etc. Finally,
itallows any user to choose among some color-theme, specific sizes
and font for text. An important limitation of BETSIE is that it has
not been possible for the BBC to offer a full text-only version of
the entire Internet, this means that BETSIE only works with BBC
sites.
The {textualise;} system [27], transforms a Web site from a
graphics-heavy and inaccessible version, to a text-only version that
is easily accessible for visually impaired users. By following the
W3C’s Web Content Accessibility Guidelines, it removes elements
that screen readers cannot handle, allows user customization of
fonts and background colors, it removes Java applets, Javascript
code, graphics and fixes ALTattributes, replaces Shockwave, Flash,
and other plug-in applications with a link to them. etc. A server
component, within the textualise; system, performs the required
transformations by using a set of transformation rules.
The Access Gateway system [7], specifically designed for people
with low vision or dyslexia, is able to handle frames (by serializing
them), tables (by linearizing them), to remove images (by substi-
tuting them with missing ALT attributes), JavaScript codes, Flash,
cookies. Another goal is how to allow speakers of other languages
to view Web pages written in these languages, when the encodings
are not supported by theirbrowsers. Itis implemented as CGI script
in C++.
WebAdapter [19] is WWW browser that provides accessibility
functionalities for blind, visual and physically impaired people.
Their idea is to include these functionalities within a browser with-
out affecting the UI for non disabled users. In particular the adap-
tations provided by WebAdapter include adaptation for physically
impaired users (customization of images sizes), adaptations for vi-
sually impaired users (turning-off of background images), and fi-
nally, adaptations for blind users (sequential presentation of tables).
Finally, WebAdapter use an integrated speech synthesizer to read
HTML documents for people with visual disabilities.
The Accessibility Transformation Gateway [23] is a transcod-

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ing gateway designed to apply on-the-fly transformations of Web
pages in order to adapt them for users with disabilities. The Web
pages, filtered by the gateway, can be easily handled and rendered
by screen readers or assistive technologies. The access gateway in-
tercepts requests/responses by applying transformations according
the accessibility and the usability rules [29]. An important step in-
clude the construction of the Document Object Model (DOM) tree
representation of the requested HTML page. Finally, some chosen
rules include: (a) providing alternate text for images, applet and
for each Object, (b) linearizing tables, (c) avoiding any URL redi-
rect and automatic page refresh, etc. Other functionalities, imple-
mented as part of the accessibility transcoding gateway project, are
simplification (i.e. deletion of clutter information on Web pages)
and summarization (building of a preview of Web pages) [22].
The IBM system described in [17] enables universal access to the
Internet content by allowing different types of devices, and people
with different abilities, to receive content that is suitable for their
needs. It removes comments and JavaScripts, handles images (by
modifying colors or removing them at all), linearizes tables, allows
text summarization. The evolution of this system led to a most fa-
mous IBM WebSphere Transcoding Publisher technology4that dy-
namically translates Web content and applications to meet different
client devices capabilities and users preferences.
Crunch [15, 16] is a Web proxy that uses a set of heuristics to
extract content from HTML pages in order to make it accessible
according to W3C Guidelines. It employs a set of heuristics, that
is filters operating on a DOM representation of a Web page, to re-
move all extraneous of useless information (not recognizable, for
example, by screen readers). In particular, the content extractor
navigates the DOM tree recursively and remove and adjust specific
nodes by leaving only the content behind. Crunch provides filters
for removing images, links, scripts, and more complex filters to re-
move advertisements, link lists, empty tables. Once entirely parsed
and adapted, the page can be rendered both in HTML and plain text
(for example for text to speech and summarization). Finally, the
Crunch is not able to handle Flash and dynamic generated codes
and to distinguish between different accessing users.
Other examples include WAB, a not customizable HTTP proxy
(based on CERN httpd) that modifies Web pages to assist blind
users. The page is transformed in a text-only version to make it
easily readable by screen readers. Tablin [26] is a filtering system,
developed by the WAI Evaluation & Repair (ER) group, that can be
used to linearize HTML tables and render them in a form suitable
for their reading from screen readers.
2.2 Intermediary Frameworks
Most Web sites, today, are designed to follow the “one-size-fits-
all” philosophy, by providing content and services without taking
care of the abilities of users that access them. In fact, because of its
increasingly complex infrastructure, the Web does not really pro-
vide equal access and equal opportunity for users with disabilities.
The documents available on the Web exhibit a growing complex-
ity, especially for people with visual disabilities, that often are un-
able to access, summarize and distill information on a Web pages
or groups of pages. For people with motor disabilities the WWW
represents a very important source of information, a familiar and
ubiquitous environment where to get information about any aspect
of life: education, employment, shopping, business, government
and more.
Hence, as the Internet continues to evolve with an increasing di-
versity and heterogeneity, there is a growing demands for techno-
4http://www-306.ibm.com/software/pervasive/transcoding publisher/
logical solutions that are able to allow the universal access to the
Web content, by breaking down the accessibility barriers that in-
hibit the access by users with disabilities. These technologies could
be provided server-side, client-side or on intermediary systems.
While server-side solution could involve several efforts for Web
designers for writing an re-designing accessible Web pages, and
client-side solution require the development of adaptive browsers
or other assistive technologies, intermediary solutions could be pro-
vided without any intervention both on client and server systems,
by allowing transcoding and Web personalization on-the-fly, trans-
parently for users with disabilities [1, 20].
By summarizing, the main advantages of edge servers systems
are that they can be transparently deployed without involving hard-
ware and/or software changes both on client and server systems,
they can reduce both complexity on servers (that will only take care
of providing the requested resources) and system requirements on
clients (independently from device’s capabilities), add new services
without stopping the servers, by ensuring their fault-tolerance, of-
fer increased flexibility (where new components can be deployed)
and scalability, and, finally, improve the quality of access to the
resources available on the Web.
Increasingly often, intermediaries have been used to develop and
deploy services for accessibility. Famous examples of interme-
diary systems that can be easily programmed to promote acces-
sibility include Muffin [http://muffin.doit.org], a Web
HTTP proxy that provides functionalities to remove cookies, kill
GIF animations, remove advertisements, add, remove, or modify
any HTML tag, remove Java applets and JavaScript code, etc.
RabbIT[http://rabbit-proxy.sourceforge.net]is
a Web HTTP proxy that accelerates the delivery of Web contents
to end users by compressing text pages and images, by removing
unnecessary parts of HTML pages (background images, advertise-
ments, banners, etc.) and, finally, by caching filtered documents
before forwarding them to the clients.
Web Based Intermediaries (WBI) [3, 4, 5] is a dynamic and
programmable framework, developed at IBM Almaden Research
Center [http://www.almaden.ibm.com/cs/wbi], whose
main goal is to personalize the Web by realizing an architecture
that simplifies the development of intermediary applications. WBI
defines a programming model that can be used to implement all
form of intermediaries, from simple server functions to complex
distributed applications.
On top of the WBI programmable proxy, as part of the more
complex SEcS:Scalable Edge-computing Servicessystem [12], has
been developed theTest-To-Speechservice [2], thatallows thespeak-
ing of the text of HTML pages during their displaying towards end
users. Moreover, the Text-To-Speech Service can help the compre-
hension of documents that are written in foreign languages, since
a reader that is partially familiar with the spoken language and not
with its written form can be supported in getting, at least, the mean-
ing of the information contained in the document. Finally, the ser-
vice can be used as a support toward kids that want to learn a lan-
guage since provides a written/spoken presentation of material of
their interest during a natural experience as navigating the Web.
The framework that has been use to develop PAN is Scalable In-
termediary Software Infrastructure for edge services (SISI): a brief
description of the framework and its functionalities are presented
next.
2.3ScalableIntermediarySoftwareInfrastruc-
ture (SISI)
The Scalable Intermediary Software Infrastructure for edge ser-
vices (SISI)[8]isa flexible,dynamic and programmable intermedi-

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Figure 1: Placement of SISI modules into the Apache request
Life-cycle.
ary infrastructure that enables universal access to the Web content.
This framework has been designed with the goal of guaranteeing
an efficient and scalable delivery of personalized services at inter-
mediate edge server on the WWW.
SISI programmability is a crucial characteristics since it allows
an easy implementation and assembling of adaptation services that
enhance the quality of services perceived by users during their nav-
igation. To allow programmability, the SISI framework provides a
programming model and a set of APIs that can be used for a quick
prototyping and a easy development of new services to improve the
navigation on the Web for not-disabled users as well as for disabled
ones. Services can be assembled and configured to enhance the set
of pre-defined functionalities.
The architecture is innovative since it provides programmabil-
ity without giving up efficiency, offers users profiles management
primitives, deployment/un-deployment and authentication/authorization
mechanisms. The work is placed on top of existing open-source
applications such as Apache Web server and mod perl because of
their quality and their wide popularity.
The SISI framework is composed of different modules, entirely
written in Perl language, each acting in a specific phase of the
Apache HTTP Request life-cycle (See Fig. 1).
The ProxyPerl Module intercepts all clients requests and initial-
izes the transaction process. Its most important task is to fetch the
requested URLs manipulating, if necessary, HTTP headers. If no
transformation has to be applied on the HTTP flow, the requested
document will be sent back unchanged to the client. Otherwise, the
transaction will be managed by the handlers invoked according to
the user’s profile.
The Authorization Module is useful both to restrict access to the
proxy server as well as to distinguish between users, so that each
user can have different SISI services applied to her requests.
The FilterPlugin Module acts as a dispatcher within the architec-
ture by activating the services according to the users’ preferences.
Finally, the Deploy Module is used by the programmer to add
new services to the framework. It consists of an automatic modules
generation process that implements intermediary services starting
from simple Perl files.
The SISI framework also provides a Graphical User Interface
implemented to simplify the management and the debugging of the
SISI components. The goal is to relieve the system administra-
tor and programmers from learning or remembering complex and
tedious commands during the administration phase and the debug-
ging of new deployed modules.
SISI user-friendly configuration of services is an important fea-
ture since in this phase the users can easily provide information
about the required services and personalize their navigation on the
Web. In fact, by allowing services configuration, SISI is able to
affect the adaptation of a given delivery context, and to change ac-
cordingly the user experience.
3.Personalizable Accessible Navigation
Personalizable Accessible Navigation, developed on top of the
SISI framework, offers to people with disabilities important func-
tionalities described below.
Configurability: each user is authenticated and services can be
applied according to the chosen configuration. Of course,
it is possible to activate/deactivate accessibility services as
preferred, by acting on a personal profile page.
Easy deployment: client-side configuration is quite simple, since
it is enough to use the proxy setting on the browser and
providing the authentication to PAN to use services. More-
over, it provides ubiquitous services from any node and does
not require installation (and therefore, administrator privi-
leges) which makes it particularly useful when accessing the
Web from public terminals as well from mobile terminals.
Our main goal is to avoid any complex and computationally
onerous browser-dependent technology [18] and provide the
same set of services to each user, in any context (be it home,
workplace or public terminal) with different devices (such as
fixed or mobile terminals).
Efficiency: the accessibility services are executed on the path
from server to client, therefore amortizing the cost of imple-
menting expensive transcoding techniques onto the “natural”
delay that is considered physiologic.
3.1 Installation
To use the PAN’s set of accessibility services, users have, firstly,
to install the SISI framework, that is available as raw source code
for Unix/Linux platforms and in a pre-compiled version for Win-
dows. The installation of the SISI framework requires the installa-
tion of the Apache Web server and mod perl, and some packages
for image manipulations (PerlMagick library) and for developing
Web client applications (LWP User Agent perl package).
The installation and the deployment of PAN is accomplished
by simply using the deployment mechanism provided by the SISI
framework (see [8] for more details).
3.2Configuration and profiles
Once deployed, the PAN set of services is accessible through a
specific configuration page (See Fig. 2).
In fact, our approach to manage user profiles is to explicit ask
the user what s/he needs and use this information with a rule-based
approach to personalize the content. In particular, users have to fill-
out forms to create new profiles and to modify or delete the existing
ones, as shown in Fig. 2.
Our user-friendly configuration of services is an important fea-
ture since in this phase the users can easily provide information
about the required services and personalize their navigation on the
Web. In fact, by allowing services’ configuration, it is possible to
affect the adaptation of a given delivery context, and to change ac-
cordingly the user experience.
When a new user is added to the system, a default profile is au-
tomatically generated and the user can modify it the first time s/he
logs into the system to choose his/her preferences.

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As an example, a user with a moderate low-vision disability
may be able to navigate with a modest help of PAN when using
his/her usual terminal (due to good indoor illumination and large-
size screen) but may need more help when accessing the network
by public terminals (i.e. ordinary-sized screens) or even more help
is needed when browsing the Web by a mobile terminal. In each
context, the user can select a different profile, previously set and
configured on PAN, obtaining the right amount of support, right
there, when he/she needs it.
Figure 2: Users’s Profile Management.
Finally, it must be mentioned that PAN is the only system that al-
lows personal configuration of services as well as multiple profiles
when compared to the systems described in section 2.1.
4.
PAN SERVICES FOR ACCESSIBILITY
The services provided by PAN are grouped in four main cate-
gories depending whether they act on text, links, images or other
objects on the HTML page (such as pop-up windows, etc.) ac-
cording, also, to the classification implicitly provided in [29]. Of
course, many of the guidelines provided by W3C for making ac-
cessible a Web site can be also found on the corresponding Best
Practices for Mobile Web [14]: as a matter of fact, dealing with
user limitations or terminal limitations can be seen as the two faces
of the same goal: promote universal access to Web resources.
4.1Text-based edge services
Here we describe two services that adapt Web pages by taking
into account the rules suggested by W3C to improve accessibility
[29] and to enhance, in general, the navigation of Web pages [28],
and, more specifically, of CSS files [9].
4.1.1
Cascading Style Sheets (CSS) files benefit accessibility since
they separate document structure fromitspresentation. More specif-
ically, they allow to define how different elements, such as headers,
text, links, etc., should appear to end users. They establish a pre-
cise control over the structure of Web pages, by providing rules for
characteristics such as spacing, alignment and positioning. They
also allow to define a precise control over text style effects such as
font size, color, and color-contrast, etc.. Finally, style sheets allow
Web designers to simplify the structure of Web pages and clean
up them by useless information and dynamic elements, by making
them more slight and more accessible at the same time (i.e. more
readable from screen readers).
The CSS-Restyling edge service
Figure 3: Form to for the CSS-Restyling edge service cus-
tomization.
Our CSS-Restyling edge service accesses the Web page retrieved
by the origin server, parses it and, for each HTML tag of the CSS
file, modifies its attribute by replacing it with accessible values as
suggested by [9, 14] . In particular, in order to deliver information
to a greater number of users, we perform the following changes:
• Font size (text and links) is changed according to service pa-
rameters (Guideline 11 in [13]);
• Text and link colors, background and foreground color com-
binations are changed toprovide sufficient contrast when viewed
by users with color deficiency (Checkpoint 2.2 Color con-
trast, Guideline 2 Text formatting and position in [13]);
• Blinking content is turned off (Checkpoint 7.2 Text style ef-
fects, Guideline 7 in [13]);
• Textual cues instead of images (by always providing for each
image the corresponding alt attribute with the content at-
tribute of the img tag, if present, or the name of the image)
(Checkpoint 3.3 Text instead of images, Guideline 3 in [13]).
The CSS-Restyling edge service applies transformations on Web
pages by taking into account both internal and external CSS files.
Thevalues provided by the CSS-Restylingservice can be customized
by the user according to his/her needs and abilities by accessing a
form on the proxy side (see Fig. 3).
An example of application of the CSS-Restyling edge service is
shown in Fig. 4.
4.1.2
The TextColor-Restyling edge service ensures that foreground
and background color combinations of Web pages provide suffi-
cient contrast when displayed to users with color deficiencies as
defined by the Guideline 2 in [29], and Section 5.3: Page Content
and Layout in [14].
The TextColor-Restyling service accesses the HTML page re-
trieved by the origin server and, for each HTML tag, analyzes its
corresponding attribute looking for background and/or foreground
text information. More precisely, the following attributes will be
taken into account: color, bgcolor, background, text, link, alink,
vlink and style’s attributes that specify images/backgrounds/colors.
The TextColor-Restyling edge service

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Figure 4: The CSS-Restyling edge service. The original WWW 2006 Website (top) and the same page with the application of the
CSS-Restyling service by PAN (bottom).

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Figure 5: The LinkAccessKey and Linkrelationship edge ser-
vices.
The main goal of this service is to adapt Web pages in order to
make them more accessible for people with color deficiencies.
4.2Link-based Services
This section include services that act on links of Web pages in
order to make Web pages more readable when users use assistive
technologies such as speech synthesizers, screen readers, etc.
4.2.1
By following the Guideline 1 defined in [29], the RemoveLink
edge service brutally removes all anchors (the HTML <A> tag)
from HTML pages, by replacing them with plain text (the text be-
tween the open and close of the anchor tag).
The main advantage of this service is that screen readers or other
vocal browsers will avoid to read useless information in Web pages
when users that access them are not able to see links and follow
them. Examples of Web pages include Web pages news, meteorol-
ogy, encyclopedias pages, etc., in which no links to other resources
are required.
The RemoveLink Service
4.2.2
The W3C Guideline 9 Design for device-independence [29], in
section Keyboard access, and the section 5.2 Navigation and Links
(5.2.6 Access Keys) in [14] state the need to use access keys HTML
elements to allow users with some disabilities to browse the Web.
Content developers should always ensure that users may interact
with a page with input devices other than a mouse. Unfortunately,
since this limitation is not often considered, we provided a solution
by developing a service that allows both motor and visual disabili-
ties users to browse the Web without limitations.
This service adds to any link embedded in a Web page a numeric
Access Key in such a way to make it accessible through a simple
combination of keyboard keys, ALT+Access Key+Return for exam-
ple (See Figs. 5 and 6). Pressing the access key assigned to an ele-
ment gives focus to the element, and the corresponding action will
be executed. In particular by pressing the access key, the browser
will follow the corresponding destination link. Moreover, the nu-
meric value of the access key is also added into the HTML source
of the Web page so it can be easily read by any screen reader. The
LinkAccessKey edge service could be useful to improve the Web
navigation on devices with limited display capabilities.
The LinkAccessKey Service
4.2.3The LinkRelationship edge Service
As defined by the W3C guideline 13 Provide clear navigation
mechanisms and by section 5.2 Navigation and Links (5.2.2 Navi-
gation Bar)in [14] content developers should use theLINKelement
and link types to describe document navigation mechanisms and
organization. Some user agents may synthesize navigation tools or
allow ordered printing of a set of documents based on such markup.
The LINK element may also be used to designate alternative doc-
uments. Browsers should load the alternative page automatically
based on the user’s browser type and preferences. For example,
content developers can produce a different content for browsers that
support “braille” rendering.
Our service adds a toolbar containing the LINK attributes on top
of each HTML page, as shown in Figure 5. It can also be useful to
make HTML pages more accessible and more readable by screen
readers, and for improving the Web navigation trough devices with
limited capabilities.
The W3C defines, other than the traditional set of relationship
links (Start, Preview, Next, Help, Bookmarks), another useful set
for Web accessibility. It includes, for example, the relationship link
Alternate, designed to provide alternative versions of documents,
the Contents link relationship, that refers to a summary or to as site
map, the Glossary, that refers to a glossary of terms contained in
the current, the Copyright, that it refers to a copyright of the current
document, etc.
4.2.4
The target attribute of the HTML A tag specifies the frame
where the document will be opened. In particular, the blank value
allow toopen a new browser window fordisplaying the correspond-
ing page.
As defined by the W3C Guideline 10 Use interim solutions [29],
new browser windows represent a critical problem for screen read-
ers because of their impossibility to jump among different pages.
Moreover, when the focus comes back on the original window, the
screen reader starts again from the begin of the page to speech the
corresponding content.
The main goal of the DeleteTarget edge service is, therefore, to
avoid any target attribute in both link and anchor elements, by dis-
playing all pages in the same browser window.
The DeleteTarget edge service
4.2.5
The LinkLinearizing edge service allows to organize and to lex-
icographically order links embedded in Web documents in order to
simplify their direct access by users with visual and motor disabil-
ities, by also adding a numerical access key (See Fig. 6).
This service parses HTML pages and places all discovered links
in a table on the top/bottom of them (as specified by the user during
the configuration and customization of the service).
The LinkLinearizing edge service
4.3 The FilterImages edge services
Web images represent a serious problem for blind users since
they cannot be read by screen readers. Moreover, particular im-
ages formats or compositions, represent a barrier also for cognitive
disabled people, as shown next.
4.3.1
The ImageRemoval edge service removes any image embedded
in a Web page by replacing it with a link to it, as suggested in
section 5.4 Page Definition (5.4.5 Non Text Items) [14].
In particular, this service parses the Web page looking for HTML
img tags, and replace them with A tags whose content attribute will
contain the link information (See image:) followed by the original
img content attribute, if it exists, and only the (See image) link
The ImageRemoval edge Service

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Figure 6: LinkLinearizing and AccessKey edge services.
message, conversely. In this way, only if requested, the image will
be displayed to end users (See Fig. 7).
Screen readers will be able ro read all important information
available in a Web page, by facilitating its comprehension by users
with disabilities.
Figure 7: RemoveImages and LinkAccesskey edge services.
4.3.2
GIF animated images represent a digital barrier for users with
cognitive disabilities. In fact, these images reduce attention from
the content, involving important problems to users that suffer of
dyslexia or of general attention deficit pathologies.
Byfollowing the Guideline 7: Ensure user controlof time-sensitive
content changes [29] we have developed a GIF-Deanimate edge
service that replaces each animated image embedded in a Web page
with a static one, by showing only its first frame.
The GIF-Deanimate service has been implemented by using the
well-known PerlMagick [24] library, that is an object-oriented Perl
interface to ImageMagick [21], a free software that allows to create,
edit, and compose images with different formats.
4.4 Easy and smooth navigation service
The GIF-Deanimate Service
4.4.1 AnnojanceFilter edge service
As defined in the Guideline 10: Use interim solutions [29] nav-
igating with several pop-up windows, banners, scripts etc., can be
difficult for people with visual and cognitive disabilities.
The main goal of the AnnojanceFilter edge service is to get rid
of particularly annoying abuse during the navigation on the Web.
More precisely, the AnnojanceFilter service provides functional-
ities for removing advertisement, banners, pop-ups in JavaScript
and HTML, JavaScript code, for disabling unsolicited pop-up win-
dows, etc. During service’s configuration users can choose the
functionality to enable by providing parameters if required.
4.4.2
The main goal of this service (based on the HTML::Clean Perl
library) is to clean HTML pages from useless or redundant code.
It is very useful for Web pages built with programs that silently
add internal code. Other functionalities include removing white
spaces (Checkpoint 3.3: Text formatting and position [13]), useless
(i.e. non-standard) META elements, HTML comments, replace
tags with equivalent shorter tags. By using the provided methods,
the service is able to reduce the size of Web pages thus speeding up
the download.
The HTMLClean service is able to ensure that documents are
clear and simple so they may be more easily understood (Guideline
14: Ensure that documents are clear and simple. [29]).
The HTMLClean edge service
5. CONCLUSIONS
Personalizable Accessible Navigation represents an efficient, ef-
fective, simple and personalizable tool to provide easier access to
the Web resources to people with disabilities. Its nature (being an
intermediary) and the characteristics of its services make it suitable
for adapting the access to Web resources in different contexts, such
as fixed/mobile terminals. Moreover, by implementing easy con-
figuration and multiple profiles PAN enhancing the usability of the
accessibility services in many different contexts.
We have realized preliminary tests in order to evaluate the effec-
tiveness of Personalizable Accessible Navigation accessibility ser-
vices. We selected a set of Web pages of international relevance,
i.e., the US White House, CNN and New York Times Web portals,
the Eclipse and Sun Web sites, and finally, the IEEE, and ACM
Organization sites.
Their Web pages are tested using the Bobby Web Accessibility
Tester(availableatthe URL:[http://webxact.watchfire.
com]) that is a comprehensive Web accessibility tool designed to
aid Web masters to test Web sites in order to improve their accessi-
bility.
Moreover, Bobby tests Web pages by using the guidelines estab-
lished in [28].
We compare the results obtained on the original Web pages by
using Bobby with the results obtained on the Web pages adapted
by PAN (by saving the adapted pages on a local server and ac-
cessing them with Bobby later on). The following PAN’s services
were tested: ImageRemoval, the CSS-Restyling, LinkAccessKey
and AnnojanceFilter. Results are showed in Fig. 8 for the original
Web pages and in Fig. 9 for the pages adapted by PAN.
In these figures we report on the Y-axis the number of errors
or warnings obtained by Bobby on each page for the categories
“Image Evaluation”, “Insufficient Color Contrast”, “Animated Ob-
jects”, “Pop-ups and new browser windows”, i.e, the lower the
number, the more accessible is the page.
The Bobby Accessibility Tester checks if analyzed Web pages
are fully compliant with all of the automatic and manual check-
points of the W3C Web Content Accessibility Guidelines. PAN,

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Figure 8: Bobby results on original pages.
Figure 9: Bobby results on PAN’s adapted pages.
instead, addresses at this time, a subset of them. This explain the
reason whereby the accessibility degree is not highly improved in
all the Web pages tested.
More precisely, the accuracy that comes out form tests is incon-
stant for Insufficient Color Contrast, Image Evaluation and Ani-
mated Objects categories since Bobby observes errors, closely re-
lated to image color contrast and Flash animations, that we do not
still have provided as services in our system. On the other hand, we
have already envisioned these functionalities, and we can quickly
implemented them, since the programmability of the SISI’s frame-
work where PAN is leveraging on.
Moreover, since the accessibility degree is highly improved in
almost the Web pages tested, our immediately important steps in-
clude further automatic tests and, in addition, detailed usability
tests in order to also estimate the effective benefits that users can
perceive during their navigation on the Web.
Finally, we must mention that the PAN location in the World
Wide Web architecture makes it usable in three different ways: the
first one is the traditional proxy setting and could be suitable for
providing public services to communities. But, PAN can also act as
an HTTP surrogate, that is as an intermediary that acts on behalf
of an origin server to provide complex functionalities, as shown in
Fig. 10 therefore adding to a non-accessible Web site the opportu-
nity to become accessible.
On the other hand, PAN, can also be placed at the other end of
the client-server path, by playing the role of an HTTP delegate on
behalf of client systems, by providing personalized functionalities
that can be also used for accessing off-line HTML repositories as
well as intranet contents (see Fig. 11).
Acknowledgments: The authors gratefully acknowledge the support and
the interesting discussions within the ISISLab. In particular, we thank
Angelo Esposito for collaborating in the implementation of CSS restyling
PAN service. Part of the research was supported by EU “Leonardo da
Vinci” project Web for handicap integrated training environment (WHITE),
I/03/B/F/PP-154143, 2003.
Figure 10: Intermediaries as logical extension of origin servers.
Figure 11: Intermediaries as logical extension of user agents.
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