Current database systems are often large and complex and the case that a user or an application has full access to the entire database is rare. It is more likely to occur that access is granted via windows of the entire systems, called
. A view, usually virtual, is defined by giving a query on the whole database and at any point the content of the view is just the outcome of this query. Applications query a base relation or a view in the same way. Therefore, querying a view does not represent a serious conceptual problem. In contrast, the issue of
is problematic and of paramount importance: it refers to the problem of translating an update request against a view into an update request involving the base of data. Over the years, a substantial amount of research has been devoted to the various issues surrounding view updating and not surprisingly a wide selection of approaches to the view update problem has evolved. See [2,3] for surveys of methods for view updating.