Bridging Ontologies and Folksonomies to Leverage Knowledge Sharing on
the Social Web: a Brief Survey
Freddy Limpens, Fabien Gandon
Edelweiss, INRIA Sophia-Antipolis, France
{freddy.limpens, fabien.gandon}@sophia.inria.fr
Michel Buffa
KEWI, Laboratoire I3S, Universite´ de Nice, France
buffa@unice.fr
Abstract
Social tagging systems have recently became very pop-
ular as a means to classify large sets of resources shared
among on-line communities over the social Web. However,
the folksonomies resulting from the use of these systems re-
vealed limitations : tags are ambiguous and their spelling
may vary, and folksonomies are difficult to exploit in or-
der to retrieve or exchange information. This article com-
pares the recent attempts to overcome these limitations and
to support the use of folksonomies with formal languages
and ontologies from the Semantic Web.
1 Introduction
To share and index the large number of resources avail-
able on the Web raises several issues that systems based
on folksonomies [27], such as del.icio.us for sharing book-
marks, have recently tried to address. On the other hand, the
Semantic Web aims at supporting the exchange of informa-
tion by developing the interoperability between applications
available on the Web. To this end, several methods, tools
and principles are proposed, among which formal ontolo-
gies play a central role. Generally speaking, ontologies are
knowledge representations aiming at “specifying explicitly
a conceptualization” [8]. More specifically, formal ontolo-
gies use formal semantics to specify this conceptualization
and make it understandable by machines. The obstacles to
a generalization of ontologies lie mainly in their cost of de-
sign and maintenance.
The aspect of the social softwares design we address
here is the need for the users of social softwares to find an
agreement about the knowledge representations that support
their collaborative use of the system. To this regard, folk-
sonomies are often seen as the bottom-up approach, while
formal ontologies of the Semantic Web are considered to
be necessarily a top-down approach. In this article we try
to show that opposing folksonomies and ontologies in this
way is counterproductive, and the works we present here
show the potential of combining both approaches in order
to collaboratively build up solid knowledge representations
that are both representative of the communities of users, and
at the same time allows for better retrieval or exchange of
information.
The Web 2.0 consists essentially in a successful evolu-
tion of the Web supported by some principles and technolo-
gies. Social tagging and the resulting folksonomies are one
of the technologies which leveraged Web 2.0 applications.
The simplicity of tagging combined with the culture of ex-
change allows the mass of users to share their annotations
on the mass of resources. However, the exploitation of folk-
sonomies raises several issues [17, 19] : (1) the ambiguity
of tags, for one tag may refer to several concepts ; (2) the
variability of the spelling, for several tags may refer to the
same concept; (3) the lack of explicit representations of the
knowledge contained in folksonomies; (4) the difficulties to
deal with tags from different languages. Another challenge
is the need to assist the life-cycle of the folksonomies and
the ontologies which support the knowledge bases of social
Web applications. Our hypothesis is that the synergy of both
folksonomies and ontologies may bring great benefits.
Research has been undertaken to tackle the problems
posed by the annotation and the exchange of the resources
on the Web. The systems or methods they propose strive
to reconcile ontology-based models and folksonomy-based
models. In section two we present the approaches aimed at
extracting the semantics from the folksonomies. In section
three we focus on the contributions that support the use of
folksonomies with the help of ontologies. In section four,
we present some systems exploiting the formalisms of the
Semantic Web to assist the exchange of knowledge, and in