A Method to obtain Information for Visually Impaired People
Juan Manuel Fernández
, Vicenç Soler
Dept. Microelectrònica i Sistemes Electrònics, Universitat Autònoma de Barcelona, Cerdanyola del Vallés, Spain
Ciber-BBN: Bioengineering, Biomaterials and Nanomedicine. Campus UAB, Bellaterra, Spain
Jordi Roig
Dept. Microelectrònica i Sistemes Electrònics, Universitat Autònoma de Barccelona, Cerdanyola del Vallés, Spain
Keywords: Web Accessibility, Table navigation, e-integration, Repairing Tools, Disability, WAI, HTML.
Abstract: Nowadays the broad use of the new technologies based on the Web gives facilities to people all over the
world, but for impaired people. This leads us to the field of Web Accessibility and one of the biggest
problems in it is the use of data tables on HTML documents. For disabled users, elements such as these and
their natural bi-dimensional structure make more difficult to navigate than for the rest of the users. In this
paper we present a solution to avoid those difficulties that disabled users find while navigating. The system
we propose is based on the way a non-disabled person visualizes the table contents, but avoiding the
processing of the images which is the natural procedure.
One of the more important problems that exist in the
field of Web accessibility is the navigation on tables.
HTML tables have a complex nature that impedes to
visual impaired people to obtain the information
contained in these elements. Moreover, the use of
standards, like World Content Accessibility
Guidelines (WCAG), is very low and therefore the
navigation on tables gets worse.
The correct design of a Web site is an unresolved
matter for the current Web content developers. A
correct use of the Word Wide Web Consortium
standards makes the navigation become easier and
friendly. The access to the information stored in the
Web can be done in a more efficiently way with the
W3C standards. We will talk about the observance
of the specific normative of the World Content
Accessibility Guidelines (WCAG) which was made
by the World Accessibility Initiative. The lack of use
of the WAI’s proposals and guidelines makes the
Web to lose all its capacity to improve the labour
and social integration of all kind of people.
Thus, we propose a solution to the correct data
table’s navigation, taking into account the stardards
of the Web. Thanks to it, we avoid the use of new
languages or specific software to read the
information of a data table as the most of the
solutions. So, the solution consists of a detection of
header’s rows and columns, that allows us offer
information regarding the relationships between the
headers and the cells of the table.
The lack of standard’s uses is a very important
problem. The HTML grammar is the base of the
Web, but it is ignored by the Web site’s developers.
One of the most important errors is the use of
HTML to offer visual information rather than CSS.
The use of both technologies allows us to offer, if
necessary, a different visualization of the
information without changing the structure of the
HTML document. A good example of that is the use
of tables to distribute the contents of the Web site.
The layout use of tables is larger than the
expected one when we started the research. Figure 1
shows a comparison over a randomly group of 487
Web pages. The search of these Web documents has
been done in an automatic way. The only condition
was that the Web site had to use the table element.
Manuel Fernández J., Soler V. and Roig J. (2008).
IMPROVING HTML DATA TABLES NAVIGATION - A Method to obtain Information for Visually Impaired People.
In Proceedings of the Tenth International Conference on Enterprise Information Systems - HCI, pages 397-400
DOI: 10.5220/0001714703970400
Use of the HTML Tables
Data Tables
Layout tables
Figure 1: How the HTML tables are used.
The bi-dimensional nature of a table offers a lot of
information. But this nature makes necessary to
know the header of the row and the column of a cell
to obtain the maximum information. The helping
tools offer the information contained on a table in a
linear list of elements. In this list, the headers
usually appear just at the beginning and they are
very difficult to remember. Our system offers the
relationship between the headers and the content of
the cell. We use HTML standard elements to
indicate these relationships.
We can classify the current proposed solutions in
three basic groups: the group where the Web
browsers adapted to offer correct navigation in
tables, new languages and the proposals which try
to modify the content of the document to mark these
4.1 Adapted Browsers
This kind of solution has a limited field of use,
because this sort of browsers can only solve one
problem. And also, the user has to learn how to use
it as well as other Web browsers. A very good
example of that is the table browser called EVITA
(Yesilada et al., 2004). Our proposal is totally
independent of the Web browser and the user does
not need to learn to use new software.
4.2 New Languages
All the solutions of this kind have the same problem:
they are not standards and the user needs specific
software to obtain the information offered. Our
proposal is based on the W3C standard. In this way
we can see, for instance, the proposals of Pontelli
and Filepp.
Enrico Pontelli and Tran Cao Son (2002)
propose the use of Domain Specific Language to
express the content of a table. This content is
extracted thanks to the semantics of the information
inside the table.
On the other hand, there exist other languages
XML based that improve the interaction between the
screen reader and the Web site. TTPML (Filepp et
al., 2002) is a language of this kind that offers all the
information to the screen reader in an easy way.
4.3 Header Detection by Means of
The Web site developer offers information about the
relationship of the table’s content in a visual way.
We can use this difference between cells to obtain
the header of a table and to relate the different cells.
The first approximation is by means of a visual
recognition after the Web page has been displayed
by the Web browser (Krüpl and Herzog, 2006). This
system has the inconvenient that it is strongly
dependent of the Web browser
The second approximation, where we are, works
with the source of the Web page. The visualization
of the Web document is marked with HTML and
CSS code and we can access to it independently
from the browser. K. Kottapally et al. (2003)
presented a system that implements this proposal.
The application implements a logic system and a
Hidden Markov Model system. The proposal has
very good results but with a very poor test set which
produces that the systems based on rules, like this
one, can fell on a situation of memorization. On the
contrary, our approximation is not based on rules to
avoid this situation. It is based on a Bayes classifier
and it will be explained in the next section.
As we have commented, it is possible to use the
visualization of the different elements of a table to
establish the existing relationships. To offer this
visual information HTML has a group of tags and
attributes that are specific to offer the visual layout.
We have made a study to obtain the use of the
different elements of a table. This study was made
over a set of 107 random data tables and the first
point to observe is the difference of the quantity of
ICEIS 2008 - International Conference on Enterprise Information Systems
align bgcolor char charoff class dir id lang style title valign
Use of the TR attributes
Figure 2: Distribution of the TR attributes.
tables belonging to both classes. The tables without
header are the most of the part, and they are twice as
the tables with headers. This fact makes, that the
dataset was imbalanced and it adds more difficulty
to the learning process.
Figure 3 shows the use of the attributes of the TR
tag. The values are standardized, and a value of ‘1’
is assigned if the value of the first row is completely
different to the rest of values of the table. A value of
‘-1’ means that the value of the first row is the same
at the entire table. The values offered in the Figure 2
are the result of the difference between the average
of the tables with and without headers.
The same process applied to the rows can be
used with the cells. We compare the horizontally
adjacent cells. This result can be compared with the
rest of the rows and we can know if the row is
visually marked with every cell (see Figure 3).
We rejected the idea of comparing all the content
of a cell to obtain difference between cells because
the same visual effect can be done with different
combinations of HTML elements. The lack of
improvement does not justify the growth of
complexity which would suppose the adding in the
Once discussed the attributes we are going to
talk about the system of learning used. We use
Naive Bayes, a method of supervised leaning,
because it is very powerful but at the same time it
has a temporal cost and the complexity is very low.
Also, this method offers the advantage of not being
affected by the unknown values of the elements.
The learning process and the tests have been done
using WEKA (Witten and Frank, 2005). This
application allows us to test our set of tables and
selection of attributes in an easy and quickly way.
Furthermore, it is developed in Java fact that allows
us to use the class, that implements the method
Naive Bayes, in the ACTAW platform (Fernández et
al., 2007). This repairing tool allows us to obtain all
the information contained in a HTML document and
modifies it in an easy way.
We saw the great number of noise that the set of
tables contain, caused by the tables belonging to the
subset of tables without headers. This fact made us
to decide to classify all the tables without
information, like tables without header. It also
complies with one of the premises of the WCAG.
We can see the results on Table 1.
Table 1: Results of the studied Subset.
Class Positive Negative % OK % Wrong
Positive 37 3 92.5% 7.5%
1 10 90.91% 9.09%
Total 92.16% 7.84%
This classification was made with a set of
learning of 50 elements and a set of test composed
by 51 elements and without noise. With this studied
distribution, the number of tables classified as tables
with header when they really are not, i.e. false
positive, is very low. Only the 7.84% was false
positive, and the correct classification is 92.15%, a
very high result.
On the other hand, and to corroborate the good
results, the system has been tested by using Cross
Validation. We use 5 subsets for the validation, and
we can see the results in Table 2.
Table 2: Results of Cross Validation.
Class Positive Negative %Ok %Wrong
Positive 68 4 94.45% 5.55%
Negative 9 20 68.97% 31.03%
Total 87.13% 12.87%
The correct classification is 87.12%, it is really
high and the false positive is so low enough. In
Table 3 we can see a comparative of the results
IMPROVING HTML DATA TABLES NAVIGATION - A Method to obtain Information for Visually Impaired People
Use of the TD attributes
Figure 3: Distribution of the TD attributes.
Offered by the cross validation and the first test In
both of them the values of g-means (Kubat and
Matwin, 1997), which is the most used measure to
evaluate results in imbalanced datasets, and the area
under the ROC curve are really good.
Table 3: Results of C. Validation and the studied Subset.
C.Validation Studied subset
G-means 0.8071 0.9170
Positive 0.869 0.941 ROC
Negative 0.869 0.941
We have presented a system of learning that allows
us to detect the headers of a table. This tool is
independent of Web browsers and compliant with
the W3C standards. With the presented method, we
can offer the relationship between the header and the
cells under its scope. This is an important
improvement because it means that the content of
the table is not only a list of elements. The table
recovers the bi-dimensional nature and allows the
impaired user to obtain all the information inside the
The proposed solution has been tested with a
heterogeneous set of real Web pages. The selection
of this set was completely random and with it we
can assure that the system does not offer good
results for only a concrete situation. The system
obtains excellent results and improves the results of
the system developed up to now.
Kubat, M, Matwin, S. Addressing the Curse of Imbalanced
Training Sets: One-Sided Selection. In Proceedings of
the 14th International Conference on Machine
Learning, 1997.
Yeliz Yesilada, Robert Stevens, Carole Goble and Shazad
Hussein. Rendering Tables in Audio: The Interaction
of Structure and Reading Styles. In Proceeding
ASSETS’04, pages 16-23, Atlanta,Georgia, USA,
Juan Manuel Fernández, Vicenç Soler and Jordi Roig.
Automatic Conversion Tool for Accessible Web. In
Proceedings of the 3rd International Conference on
Web Information Systems and Technologies, pages
459-462. Barcelona, Spain, 2007.
Enrico Pontelli and Tran Cao Son. Planning, Reasoning,
and Agents for Non-visual Navigation of Tables and
Frames. In International ACM SIGCAPH Conference
on Assistive Technologies pages 73-80. Edinburgh,
UK, 2002.
Robet Filepp, James Challenger and Daniela Rosu.
Improving the accessibility of aurally rendered HTML
tables. In International ACM SIGCAPH Conference
on Assistive Technologies pages 9-16. Edinburgh, UK,
Bernhard Krüpl and Marcus Herzog. Visually Guided
Bottom-Up Table Detection and Segmentation in Web
Documents. In Proceeding of International World
Wide Web Conference, pages 933-934, Edinburgh,
UK, 2006.
K Kottapally, C. Ngo, R. Reddy, E. Pontelli, T.C.Son and
D.Gillan. Towards the Creation of Accessibility
Agents for Non-visual Navigation of the Web. In ACM
Conference Universal Usability, pages 134-141,
Vancouver, Canada, 2003.
Ian H. Witten and Eibe Frank. Data Mining: Practical
Machine Learnign Tools and Techniques 2
Edition.Elsevier, San Francisco, USA 2005. ISBN: 0-
ICEIS 2008 - International Conference on Enterprise Information Systems