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

 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

manager

DIG interfacing

library

Web

-driven

GUI

web browser hostin

environment

external

reasoner

ontology

database

(.owl files)

Management

Professors

Technical

Facult

(prof_resp_for_lab) Laboratories

(

belon

s_to_de

)

artments

Figure 3: ContextMenu for “Professors” class.

Figure 2: browsing application screenshot.

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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.

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Pietriga, E., 2002. “IsaViz, a visual environment for

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Farquhar, A., Fikes, R., Rice, J., 1996. “The Ontolingua

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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

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V. Geroimenko, (Ed). Springer.

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