Notes on View Synchronization using Default Logic ( Extended Abstract )

The synchronization of views is one of the schema evolution problems and it calls for the rede nition of those views becoming undened after a schema change, in order to keep them still working on the new schema. This problem is particularly di cult for capacity reducing schema changes, when it could be only possible to approximate the existing views. Recently, the use of schema mappings to express schema changes has allowed both to deal with a wide range of schema change operations and to facilitate the view synchronization; but approximating views requires mappings able to describe approximate schema changes. This paper introduces the default schema mappings, a new kind of mappings based on default logic and it provides a preliminary study showing the possibility of using them to realize an approximate view synchronization process.