SEMANTIC WEB BROWSING
Ioannis Papadakis
Libraries and Archives Department, Ionian University, Plateia Elftherias Corfu 49100, Greece
Michalis Stefanidakis
Computer Science Department, Ionian University, Plateia Elftherias Corfu 49100, Greece
Keywords: Semantic web, ontologies, browsing, web, OWL, Ajax.
Abstract: The employment of semantic web technologies like ontologies, give the opportunity to web engineers to
model the information space of web sites according to the conceptualization of the broader domain they
refer to. In this paper, an innovative highly interactive semantic web browsing methodology is presented,
that is applicable to a wide range of current web sites of rich and at the same time diverse content. The
proposed approach is demonstrated through a prototype semantic web application based on current web
technologies such as OWL and Ajax.
1 INTRODUCTION
Current semantic web applications seem not to be
appealing to average web users since they transfer
the complexity of semantic web technologies (i.e.
OWL (www.w3.org/2004/OWL), RDF
(www.w3.org/sw/RDF), ontologies, etc) to the
Graphical User Interface – GUI). Consequently,
average web users that are not (and should not be)
accustomed to the specialized vocabulary that is
employed by semantic web engineers, fail to
appreciate the benefits of the provided functionality.
Having the above thoughts in mind, this paper
introduces a highly interactive methodology for
browsing web sites based on semantic information.
Such information is described through ontologies
encoded in OWL format. More specifically,
depending on an underlying ontology, users are able
to take control over their browsing habits by
focusing on a specific part of the web site’s
information space.
The proposed methodology is demonstrated
through the implementation of a prototype web
application based on Ajax technology (Paulson,
2005). It consists of an interactive browsing
interface that communicates with an ontology
encoded in OWL format. The ontology’s complexity
is transparent to end users, since the GUI consists of
distinct visualization elements (i.e. widgets) that are
familiar to average web users. Reasoning with the
ontology is facilitated through an open source
reasoner (i.e. Pellet (www.mindswap.org
/2003/pellet/)) and the standard DIG interface
(Bechhofer, 2003).
The rest of the paper is structured as follows:
section 2 outlines the most important issues that
arise when visualizing semantic information,
especially on the web. Section 3 presents the
prototype semantic web application through an
appropriate case study. Finally, the last section
concludes this paper and points directions for future
work.
2 VISUALIZING SEMANTIC
INFORMATION
The initial attempts towards visualization of
semantic information produced software that was
delivered to end users through desktop applications.
In this direction, the IsAViz tool was designed to
visualize RDF graph-based structures (Pietriga,
2002). One of its key features is the fact that, in
addition to showing instances, IsAViz shows
connections from instances to their originating
classes. Although such a tool is suitable for
authoring RDF structures, it lacks usability when it
is employed in browsing through metadata since
users are overwhelmed with too much information
and constantly crossing edges.
400
Papadakis I. and Stefanidakis M. (2007).
SEMANTIC WEB BROWSING.
In Proceedings of the Third International Conference on Web Information Systems and Technologies - Web Interfaces and Applications, pages 400-403
DOI: 10.5220/0001276204000403
Copyright
c
SciTePress
A visualization technique suitable for ontologies
is the "Cluster Map" developed by the dutch
software vendor Aduna (www.aduna.biz). The
cluster Map technique (Fluit et al, 2002) focuses on
visualizing instances and their classifications
according to the concepts of an underlying ontology.
It is suitable for light-weight ontologies that describe
a domain through a set of concepts and their
relationships. Although such an approach scales
relatively well for small to medium-sized ontologies,
it is only suitable to ontologies featuring hierarchical
relationships between their underlying concepts.
The solutions presented so far are all more or less
featuring desktop standalone implementations,
capable of taking the full advantage of various
programming environments.
However, in order to realize Tim Berner Lee’s –
TBL’s vision about the semantic web (Berners Lee
et al, 2001), semantic applications should be readily
available to users with minimum effort. Web-based
solutions fulfill this requirement, since they have
minimal technical prerequisites (a common web
browser will do) and users are already accustomed
to the overall web environment.
In this direction, the Ontolingua system
(Farquhar et al, 1996) is an ontology editor and
browser based on HTML widgets. Such a tool is
better suited to knowledge Management – KM
experts rather than common users, since it requires
specific skills from the KM community. Like many
others, Ontolingua employs edges and nodes to
represent concepts and their relationships.
A more sophisticated approach concerning the
visualization of ontologies is introduced by CNET's
news.com online news site
(news.com.com/The+Big+Picture/2030-12_3-
5843390.html). Their ontology browsing system
developed by www.liveplasma.com employs
Macromedia flash technology to visualize concepts
and relies on different colours to distinguish
individuals that belong to different classes.
However, their node-edge approach overwhelms
users and the lack of zooming restricts the
representation of the ontology to a minimum number
of concepts and individuals.
It seems that current approaches at the field of
semantic web are designed having in mind the
requirements of KM experts rather than average
users. In order to bring the semantic web closer to
the public, this paper introduces a semantic web
browsing methodology suitable to serve the average
web user. As it will be described in the following
sections, the interactive GUI that delivers the
proposed functionality to the web browser, gradually
visualizes an underlying ontology in OWL format
through the employment of common HTML widgets
and the most promising Ajax technology.
3 SEMANTIC WEB BROWSING
APPLICATION
The proposed semantic web methodology is
presented through a prototype semantic web
application that visualizes ontologies in OWL
format. Communication between the client-side
browsing service and the server-side knowledge
database is facilitated through a translation process
between user-generated requests and formal
semantic queries.
The design of the browsing application is defined
by the following disciplines:
1. Ontological terms, while being valuable to
authors of the knowledge database, should remain
invisible to end users.
2. The number of widgets participating in the
user interface is small. Each widget has well-defined
functionality. This way, average users can
familiarize themselves easier with the interface and
be more effective in their search for information.
3. In order to facilitate quick navigation and fast
retrieval within the underlying information space,
the proposed application provides a rich set of
relationships between concepts of the underlying
ontology. This is done in an informal and at the
same time intuitive manner, via familiar hypertext
links and context menus.
4. Finally, the application is based on the
ubiquitous web browser interface in order to be
accessible to a great number of users in platforms
with different architectures and operating systems,.
The prototype application is based on the
following architecture (see fig. 1):
The KB manager and the web-driven GUI are
integrated into a web-based Ajax application. Pellet
is employed as an external reasoning engine,
touched via the standardized DIG interface
(Bechhofer, 2003). Sample test-case ontological
facts are read from files in OWL format. The
application’s components and their corresponding
functionality are explained in detail in the following
paragraphs.
3.1 The Ontology KB Manager
The ontology KB manager module is a key part of
the application with multiple functionalities:
SEMANTIC WEB BROWSING
401
1. When the browsing process is initialized by a
user, the ontology KB manager loads the ontological
Figure 1: The architecture of the prototype application.
facts from adequate files. Such files are parsed and
asserted facts are sent in an appropriate form to the
external reasoner, via the DIG interfacing library.
2. The KB manager constructs a local graph of
the ontology structure. Such a graph contains only
part of the overall information space. This way, the
web-based application is not overloaded, since the
user’s web browser doesn’t host heavy data
structures, in the case of large ontologies. Yet, due
to the fact that the current DIG specification cannot
convey information about the structure of an
ontology back to the application, it is obligatory to
keep information locally about domains and ranges
of ontology relations, as well as connection between
inverse relations.
3. After the initialization phase, the ontology
KB manager acts as a translator of user requests to
the ontology and vice-versa. In case of locally
satisfied requests, results are immediately returned
to the user. In any other case, the appropriate DIG
query is forwarded to the external reasoner.
3.2 Semantic Browsing GUI
Interaction between users and ontologies is realized
by means of four visual widgets:
a) A ClassBox describing a class of the ontology
(see outer green box in fig. 2). The items within are
the direct subclasses of this particular class. The user
may navigate to a subclass repeatedly, all the way
down to the bottom of the class hierarchy.
b) A ContextMenu (an example is shown in fig.
3), which is used to list all available relations
(except of the subclass-Of relation), for a given class
having the role of a “domain”. The ContextMenu is
activated by right-clicking on a subclass widget of a
ClassBox. The ability to navigate through the
knowledge base according to the inferred relations
of the ContextMenu instead of mere hierarchical
subclass paths, is the true strength of the proposed
interface.
The content of a ContextMenu is returned by the
KB manager itself, which tracks domains and ranges
of relations.
c) An interconnecting LinkLine, employed to
denote the type of relation between two adjacent
ClassBoxes. The LinkLine conveys this information
via its label and positioning (see green lines in fig.
2).
Two distinct cases are possible, depending on the
previous action of the user:
i) In the first case, the user navigates to the last
ClassBox selecting a particular subclass widget of its
parental ClassBox. The LinkLine’s label (i.e.
“contains” in fig. 2) depicts a subclass-Of relation.
Moreover, the positioning of LinkLine at the level of
both ClassBoxes’ class name headers denotes a
relation between these classes.
ii) In the second case (right side of fig. 2), the
user selects a relation from the ContextMenu (see
fig. 3) of a specific subclass widget of a ClassBox.
The newly created ClassBox describes a class that is
web based (AJAX)
application
Ontology
KB
manager
DIG interfacing
library
Web
-driven
GUI
web browser hostin
g
environment
external
reasoner
ontology
database
(.owl files)
Management
Professors
Technical
Facult
y
(prof_resp_for_lab) Laboratories
(
belon
g
s_to_de
p
t
)
De
p
artments
Figure 3: ContextMenu for “Professors” class.
Figure 2: browsing application screenshot.
WEBIST 2007 - International Conference on Web Information Systems and Technologies
402
the range of the selected relation. The label on
LinkLine contains the name of this particular
relation, while the LinkLine height has been
adjusted to indicate the subclass of the previous
ClassBox, as this subclass is the domain of the
depicted relation.
d) An IndividualPane, an informational area
listing the “search results” for individuals belonging
to a selected class of the ontology (see down-right
part of fig. 2). These individuals are the actual
targets of users’ browsing actions. The term “search
results” has two different meanings, in the same
context as previously presented for LinkLine:
i) When a user navigates by selecting a direct
subclass, the IndividualPane is connected to the last
(most right) ClassBox displayed. The deriving
information contains all individuals belonging to the
class of this last ClassBox (i.e. current class). As this
is inferred information, the KB manager requests
from the external reasoner all instances of the
current class in order to fill the listing area.
ii) In the case of navigation via a ContextMenu,
the results displayed on the IndividualPane combine
the last two ClassBoxes. These two classes are
domain and range of the relation shown on the
LinkLine between ClassBoxes. The IndividualPane
lists now individuals related through the particular
relation (down-right corner of fig. 2). For the
extraction of this information the KB manager a)
requests first from the external reasoner all instances
(individuals) of domain class and b) in a combined
request asks for each received individual about other
instances (roleFillers) connected to it via the selected
relation.
3.3 DIG Interfacing Library Routines
The DIG interfacing library is actually a simple
wrapper based on the DIG 1.0 specification that
issues asynchronous HTTP requests responsible for
exchanging data in XML format between the
application and the Pellet reasoner. No complex
state is kept into this interface, as it is used merely
for forwarding data between the ontology KB
manager and the external reasoner.
4 CONCLUSIONS
In this paper, a semantic web browsing application
has been presented. Specifically, the underlying
resources are organized according to the
conceptualization of the overall domain. Thus,
resources are attached to interrelated concepts as
opposed to current practice dictating that resources
should be organized in classes based on the
similarity of their content.
The proposed approach is demonstrated through
a prototype implementation based on semantic web
technologies such as ontologies and reasoners, as
well as web technologies like Ajax, capable of
eliminating many of today’s web drawbacks.
Moreover, the functionality of the approach has been
further investigated through a case study that
provides a web browsing interface to a sample
University infrastructure. The underlying domain is
conceptualized according to an OWL-DL ontology
and the GUI is delivered through Ajax technology.
Interaction between the ontology and the GUI is
facilitated through the Pellet reasoner and the DIG
interface.
Future work will be focused at extending the
proposed semantic browsing methodology in a way
capable of exposing editing capabilities to the
underlying ontology. The ultimate goal is to provide
an easy to use, multi-purpose, modular web interface
between average internet users and sophisticated
semantic technologies like ontologies.
REFERENCES
Pietriga, E., 2002. “IsaViz, a visual environment for
browsing and authoring RDF models”. In 11th
International WWW Conference Developers Day.
Farquhar, A., Fikes, R., Rice, J., 1996. “The Ontolingua
Server: a Tool for Collabo-rative Construction”.
Computer Science Department, Stanford University,
Ed: BR. Gaines and MA. Musen.
Berners Lee, T., Hendler, J., Lassila, O., 2001. “The
Semantic Web”. In Scientific American, Vol. 284 No
5, pp. 34–43.
Bechhofer, S., 2003. “The DIG description logic interface:
DIG/1.1.” In Proceedings of the 2003 Description
Logic Workshop (DL 2003).
Paulson, L. D., 2005. “Building rich web applications with
ajax”. In IEEE Computer, Vol. 38 No. 10 pp. 14–17.
Fluit, C., Sabou, M., van Harmelen, F., 2002. “Ontology-
based Information Visu-alization:Towards Semantic
Web Applications”. In Visualizing the Semantic Web,
V. Geroimenko, (Ed). Springer.
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