On the Use of FOAF in Semantic Web Portals

Position Paper for the 1st Workshop on Friend of a Friend, Social Networking and the Semantic Web

1-2 September 2004, Galway, Ireland

Authors:

Last Changed: 20 July 2004

Abstract
1. Introduction
2. Reasons for integrating FOAF
3. Current Work
Outlook
References

Abstract

In this position paper, we will briefly present our reasons for and approach in integrating the FOAF vocabulary into an ontology which serves as the conceptual backbone of a Semantic Web Portal. The integration was done by restricting the use of FOAF's concepts and properties on the one hand, and by augmenting them with our own concepts and properties on the other hand.

1. Introduction

DERI's Semantic Web Portal Working Group is currently developing a SWP platform for scientific communities, covering areas such as research, education, etc. According to Lausen et. al. (see [Lausen et al., 2004]) a semantic web portal (SWP) is defined as a web portal

for a community to share and exchange information
developed based on semantic web technologies

The conceptual backbone of a Semantic Web Portal is an ontology, which helps to structure and organize the portal's domain into its various concepts and relations. By explicitly formalizing the ontology in an ontology language such as OWL, the portal can use a number of existing tools such as APIs, reasoners, query interfaces, etc. to facilitate automatic information exchange in the context of the Semantic Web. While working on the ontology for our specific SWP (see [Moeller and Predoiu, 2004]), we decided to integrate the FOAF vocabulary. Section 2 of this paper will discuss the rationale behind our decision for doing so and give some examples of the practical benefits. Following that, section 3 will describe in more detail how we make use of the various concepts and properties defined in the FOAF specification (see [FOAF-SPEC]).

2. Reasons for integrating FOAF

Generally speaking, we had three main reasons for integrating FOAF into our ontology:

Reuse: an ontology for SWPs must cover the concepts, entities and relations within the domain of an SWP, e.g. persons, organizations, documents, events, etc. Between this domain and the domain that FOAF covers, there is quite a wide overlap. This makes it a natural decision to simply take advantage of the work and efforts that have went into the development of FOAF.
Consensuality: From our point of view, using FOAF would increase the acceptance of our own ontology, since FOAF is already well-known and relatively widely in use. From the point of view of the FOAF standard, it is desireable that it is used in as many places as possible. In other words, by integrating FOAF into our ontology, we help setting and strengthening the FOAF-standard.
Interoperability: from a pratical point of view, using FOAF makes it easier to integrate existing data and provide data to agents who are already FOAF-enabled.

In the following paragraphs we will give some example scenarios to illustrate just how the SWP will benefit from the integration of the FOAF standard.

Imagine a researcher who wants to register himself to a SWP for his field of research. In a conventional web portal, he would now have to fill in a form containing various data about his person, such as his name, degrees, etc. However, if the portal understood FOAF, he could register by simply providing a link to his FOAF description.

From a different perspective, the portal would provide a public query interface (e.g. an RDQL-interface), through which FOAF-crawlers or FOAF-enabled agents could access its Knowledge Base. In this way, the portal's data is added to the global semantic web.

3. Current Work

We developed an ontology for a SWP (see [Moeller and Predoiu, 2004]) that is intended to be used as a platform for the exchange between all kinds of people working in the area of the Semantic Web. As the FOAF vocabulary didn't fit exactly to our purposes, we had to find ways to both specify and generalize it. By specifying we mean to add subclasses and additional properties to FOAF concepts where required. Naturally, the SWP ontology also comprises a number of other classes, that are in no hierarchical relationship to the FOAF classes. By generalizing we mean to restrict the set of FOAF classes and properties to be used in the SWP. Furthermore, we generalize FOAF classes by adding new super classes to them.

In the following, we give some examples of our adaptation of the FOAF vocabulary.

adding subclasses: We specified the FOAF class Person by adding subclasses like Researcher, Developer and the like to model the different kinds of persons we wanted to distinguish between.
adding properties: In order to relate FOAF instances to instances of other classes, we had to introduce a number of new properties. E.g., we added a property organizes, which has the FOAF class Agent in its domain and the new class Event as its range.
ignoring FOAF classes and properties: while there certainly is a wide intersection between the domain of the FOAF specification and the domain of the SWP ontology, the former is not a subset of the latter. Therefore, there are a number of FOAF classes and properties that have no relevance in our SWP. FOAF data containing such classes and properties (e.g. OnlineGamingAccount, icqChatID, holdsAccount, etc.) could still be imported - however, the elements in question would simply be ignored by the portal.
adding new superclasses to FOAF classes: Even though the foaf:Document class is already quite general, we decided to generalize it even further by adding a superclass Publication. The reasons for doing this arose from the fact that we also wanted to cover specific kinds of collections of documents in our ontology (e.g. Proceedings, Series, etc.). These collections are subsumed by the PublicationContainer class. Eventually, to properly model the connection between both classes, we introduced a common super class.

4. Outlook

The SWP ontology as well as the SWP itself are still very much work in progress. Future work in the implementation of the portal will reveal whether or not our approach was useful and viable.

References

[FOAF-SPEC] D. Brickley and L. Miller: FOAF Vocabulary specification. Available at http://xmlns.com/foaf/0.1/

[Moeller and Predoiu, 2004] K. Möller and L. Predoiu: Semantic Web Portal Ontology v0.9, Project Deliverable, Digital Enterprise Research Institute, 2004. Available at http://www.deri.at/research/projects/sw-portal/papers/deliverables/D1-PortalOntology-v0.9.pdf

[Lausen et al., 2004] H. Lausen, M. Stollberg, R. L. Hernandez, Y. Ding, S.-K. Han, D. Fensel: Semantic Web Portals - State of the Art Survey, Technical Report, University of Innsbruck, 2004. Available at: http://www.deri.at/research/projects/sw-portal/papers/publications/SemanticWebPortalSurvey.pdf