Possible supervisors: Marta Sabou and Michel Klein
How ontologies change
Once ontologies became the metadata for the Semantic Web, they are no longer regarded as static but rather as dynamic domain descriptions. At the VU there are two projects dealing with ontology changes: Ontology versioning (Michel Klein)  and Ontology evolving in p2p environments (Ronny Siebes) .
The ClusterMap algorithm visualises a set of classes, their hierarchical relationship and the instancies of a data set. The technique supports user tasks such as data analyses, querying and web-navigation . A task that has not been explored yet is monitoring: representing the same ontology at different moments in time, so that the changes are visible.
The project explores the monitoring power of the Cluster Map and its applicability in one or both projects. We seek answers to the questions: what ontology changes can we visualise? How to show these changes? In what scenarios can monitoring be useful?
S1) Look around for other ontology change visualisers - this would be a part of the literature study and would familiarise you with the field and the problems other people had. (for example Michel's OntoView)
S2) What is a change and what sort of changes can occur in an ontology? (Add/remove classes/instances/properties, class-merge, class-division etc). Look in the work of Michel and Rony. (Note that we can show only changes at the conceptual level.)
S3) Which of these changes can be visualised with the ClusterMap? (only for Frank and Chris) We usually show ontology classes, class-hierarchy and data instances. Therefore changes that involve properties cannot be shown. However, we could assign different ontology elements to the ClusterMap elements: for example we consider properties as data items - in this way it should be possible to show how properties are added/deleted to classes.
S4) How to show changes? Different settings can be used for the elements of the maps (their form, color, size, as well as transitions from a state to another - animated or sudden). Which of these would be useful to underline the differences between versions? Think of several monitoring methods. Do you have new ideas that could be implemented in the future?
S5) Applicability: Think of some usage scenarios for monitoring (ex. As aid for distributed ontology building).
C1) The ontologies are usually represented in RDF/DAML+OIL. Meanwhile the input format of the ClusterMap is an XML document that describes classes, instances and their relationships. It would be very handy to have an RDF2MM transformer. This could produce different ontology views (see point S3) - I think there is already some work done about this (Chris?)
C2) Develop a simple application which implements some of the monitoring methods.
1 Michel Klein and Dieter Fensel: Ontology versioning for the Semantic Web In Proceedings of the International Semantic Web Working Symposium (SWWS), Stanford University, California, USA, July 30 - August 1, 2001.
2 R. Siebes. LARiSSA: a Prototype Implementation for Evolving Ontologies. Master's thesis, Vrije Universiteit Amsterdam, aug 2001.
3 Ontology-based Information Visualisation (VSW'02) Christiaan Fluit, Marta Sabou and Frank van Harmelen.