This is part of a paper we recently presented at the ONTORACT
workshop. I think this may be relevant for some of the OOR
discussions. If I can I will upload the paper as such into the wiki.
Cheers. (01)
As The Semantic Web (SW) envisions a metadata-rich Web where
human-readable content will have machine-understandable semantics
there has been an increasing number of OWL ontologies [1] responding
to those knowledge representation requirements. Wang et al collected
1275 files, both OWL and RDF schemas, in 2005; a more recent counting,
based on web crawling, gave an impressive result of over 6000
validated OWL ontologies (Backer et al, unpublished data); by the same
vein Swoogle [2] hosts 2,563,125 Semantic Web Documents (SWD) [3].
These growing numbers, which reflect the intrinsic need of the SW for
ontologies, have fostered a number of research projects aimed at
supporting re-usability, better modularization as well as intelligent
storage and retrieval for the encoded knowledge. To this end the
design and development of an agreed upon metadata for describing
ontologies is critical. Several repositories should be able to
facilitate not only the discovery of reusable components, entire
ontologies or just portions of them, but also interoperability across
repositories. In a recent effort to unify the description of
ontologies, the Ontology Metadata Vocabulary Consortium [4] proposed a
set of descriptors that follows the principles of the Dublin Core.
This is a step in the right direction as most ontologies exist without
any additional information in the form of metadata. We advocate the
use of OMV and support further refinements and extensions of this
proposal. Although the extensions we propose for the Ontology Metadata
Vocabulary (OMV) [4] are, in principle, domain independent, our main
interest lies in supporting repositories with a particular focus on
supportive applications for elderly and disabled people. As part of
the OASIS project (Open architecture for Accessible Services
Integration and Standardization) [5], we are currently developing a
repository for ontologies aiming to describe spatial-temporal
scenarios as well as medical and technological information related to
elderly and disabled populations, i.e. users with special needs.
Within this context we are working on a repository of ontologies that
provides structured access and easy-to-extend descriptions for the
ontologies it hosts. The following principles are important when using
metadata for structuring ontology repositories: i) ontology standards
should be kept intact; ii) the metadata-core is connected to various
meta-descriptions through alignments ? mediators; iii)
meta-descriptions structure specific parts of knowledge; iv)
meta-descriptions need to support query languages and reasoning; v)
meta-descriptions may again be ontologies. (02)
Repositories, within the context of the SW, should offer more than
just data storage. The Ontolog community, a virtual community of
practice of ontology experts, discussed the matter and agreed that the
purpose of an Open Ontology Repository (OOR) is to provide an
architecture and an infrastructure that supports: a) the creation,
sharing, searching, and management of ontologies, and b) linkage to
database and XML Schema structured data and documents [5]. Currently
there are some ontology repositories over the web, however none of
them complies with those requirements agreed upon during the last
Ontolog Summit [6]. For instance, Swoogle provides a single
entry-point to several semantic web documents (ontologies), but does
not offer any validation, as there is no quality control over the
exposed material; nor does it facilitate query or editing operations.
Swoogle?s query approach for finding ontologies is based on (sub)
string search and link-based reference counting; once the document has
been found it doesn?t support any further operation. It also allows
the composition of queries via the REST interface. OntoSelect [7]
offers a similar approach; it presents the user with a basic overview
of web-accessible ontologies. The collection can be browsed by:
ontology name (derived from owl:Ontology/rdfs:comment); format (from
the ontology URL); human language (from rdfs:label); number of labels,
classes, properties, or included ontologies (owl:imports). Currently
OntoSelect hosts 1530 ontologies. The TONES repository, developed as
part of the TONES project [8], hosts 185 ontologies. It aims to
provide a reasonable amount of ontologies for testing purposes,
emphasizing reasoning techniques. This repository also supports the
REST interface for programmatic access. Ontologies can be selected and
sorted by means of metrics for expressivity, class and property
restrictions and axioms, logics, and individuals. A novel approach is
provided by Rubin et al [9] with Bioportal. Not only does it provide
access to several ontologies, but it also facilitates online editing
operations such as annotation of ontologies in the form of marginal
notes ?currently only available for classes. In [10], a lightweight
metadata ontology for an ontology repository of a multiagent system is
presented. The ontology consists of four classes: Conceptualization,
Ontology, Person, and Representation. The Ontology is described by a
title, version number, language, author, and textual description. The
Person defines the author of an ontology, while the Conceptualization
class defines an abstract view, on which the ontology is based. The
class Representation specifies the encoding of Ontology, Person, and
Conceptualization. This repository also supports the REST interface.
Although existing ontology repositories aim to provide access to
semantic web documents by means of similar query facilities, they
diverge in the methods and techniques employed for gathering these
documents and making them available; each one of them interprets and
uses metadata in a different manner. For instance, Swoogle defines
three categories of metadata; (i) basic metadata, which considers the
syntactic and semantic features of a ontology, (ii) relations, which
consider the explicit semantics between individual ontologies, and
(iii) analytical results such as SWO/SWDB classification, and
ontologies [2]. Both, TONES and OntoSelect, also rely on structural
metadata; however, the use of this metadata is limited to a subset of
it. As Bioportal supports the involvement of communities of practice
it makes use not only of structural metadata but also of that metadata
describing how the community has engaged. For instance, descriptions
of those who have defined a new relationship by means of a marginal
note in a way that it facilitates to establish rankings of confidence. (03)
Alexander Garcia
http://www.usefilm.com/photographer/75943.html (04)
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