Transaction management One important task is the implementation of a transaction management to avoid problems when multiple users edit the ontologies and commit their changes simul- taneously. However, since our system stores the different ontologies in a database back end, the concurrency control will probably be solved on the database level. In addition, we think about implementing a locking mechanism on the subtree or ontology module level to avoid inconsistencies.

Conflicts When different members of a community collectively extend an ontology, different opinions inevitably can cause conflicts to occur. Consequently, a conflicts resolution is an essential functionality. We plan to solve this problem using a combined approach consisting of a community-based and a role-based conflicts resolution strategy similar to the one proposed by Li et al. in [4].

Duplication of concepts In order to avoid dublicated concepts, we already implemented a search engine for the UbisWorld system, which can be used to find classes, instances and properties of the UbisOntology. This is a very important feature with regard to the editing process using UbisEditor. When a user plans to insert a new element into the UbisWorld ontology, but is not sure whether an appropriate concept already exists, the UbisSearch can be used to remove ambiguity.