1 Ontology Evolution within Ontology Editors Presentation at EKAW, Sigüenza, October 2002 L. Stojanovic, B. Motik FZI Research Center for Information Technologies at the University of Karlsruhe, Germany

2 Agenda Introduction Requirements Evaluation Conclusion

3 Introduction Ontology editors are main tools for ontology development Ontologies must be able to evolve for a number of reasons, including the following:  Application domains and user‘s needs are changing  System can be improved An ontology editor has to support ontology evolution

4 Agenda Introduction Requirements Evaluation Conclusion

5 Requirements for Ontology Evolution Functional requirement User’s supervision requirement Transparency requirement Reversibility requirement Auditing requirement Ontology refinement requirement Usability requirement

6 Functional requirement - specifies which functionality must be provided for the ontology development and evolution - depends on the underlying ontology model

7 Functional requirement Composite changes  They are more powerful  They have coarser granularity  They have often more meaningful semantics e.g. Move_Concept  (RemoveSubConcept + AddSubConcept)

8 Functional requirement

9 User‘s supervision requirement ProjectPerson Student HiwiPhDStudent X Critical situations:  how to handle orphaned concepts;  how to handle orphaned properties;  how to propagate properties to the concept whose parent changes;  what constitutes a valid domain of a property;  what constitutes a valid range of a property;  whether a domain (range) of a property can contain a concept that is at the same; time a subconcept of some other domain (range) concept;  the allowed shape of the concept hierarchy;  the allowed shape of the property hierarchy;  must instances be consistent with the ontology. - enables the user-driven process of change resolving - delete - reconnect to the root - reconnect to the superconcepts

10 Transparency requirement - provides a human-computer interaction for evolution by: presenting change information in an orderly way allowing easy spotting of potential problems alleviating the understanding of the scope of the change

11 Reversibility requirement Remove Concept Add Concept X - states that an ontology editor has to allow undoing changes at the user’s request

12 Auditing requirement - allows inspecting the performed changes by: keeping a detailed log of all performed changes associating meta information with each log change tracking the identity of the change author

13 Structure-driven –exploits a set of heuristics to improve an ontology based on the analysis of the ontology structure Data-driven - detects the changes based on the analysis of the ontology instances Usage-driven – takes into account the usage of the ontology If no instance of a concept C use any of the properties defined for C, but only properties inherited from the parent concept, we can make an assumption that C is not necessary. By tracking when entity has last been retrieved by a query, it may be possible to discover that some entities are out of date Ontology refinement requirement  If all subconcepts have the same property, the property may be moved to the parent concept  A concept with a single subconcept should be merged with its subconcept.  If a direct parent of a concept can be achieved though a non- direct path, then the direct link should be deleted.

14 Usability requirement - states that an ontology editor should: be ergonomically correct to minimise human errors detect logical conflicts (verification) provide the means for validation

15 Agenda Introduction Requirements Evaluation Conclusion

16 Evaluation “-“ - no support “<>” – partial support “+” - full support

17 Agenda Introduction Requirements Evaluation Conclusion

18 Conclusion Ontology editors should: enrich the list of possible changes enable the customisation of the change resolving inform the user about all effects of a change allow undoing changes allow inspecting the performed changes suggest the user to generate a change identify inconsistency and provide answers to the questions such as how, why, what if, etc.

19 Resolution points Elementary evolution strategies

20 Thanks! Any questions? L. Stojanovic, B. Motik FZI Research Center for Information Technologies at the University of Karlsruhe, Germany