On the updatability of XML views over relational databases

XML has become an important medium for data exchange, and is also used as an interface to – i.e. a view of – a relational database. While previous work has considered XML views for the purpose of querying relational databases (e.g. Silkroute), in this paper we consider the problem of updating a relational database through an XML view. Using the nested relational algebra as the formalism for an XML view of a relational database, we study the problem of when such views are updatable. Our results rely on the observation that in many XML views of relational databases, the nest operator occurs last and the unnest operator does not occur at all. Since in this case the nest operator is invertible, we can consider this important class of XML views as if they were flat relational views.