Users frequently wish to think about their data in terms of XML, even though
the data may actually be stored using a relational database.  Therefore, much
recent work has focused on the problem
of querying relational databases through XML views.  The question of updating relational databases through XML views,
however, has received less attention.
 
Using a notion of query trees to capture the salient features of most XML query languages (such as nesting and
heterogeneous sets), we describe how XML views expressed using query trees can be mapped to a set of corresponding
relational views.  We then show how updates on the XML view are mapped to updates on the corresponding relational
views.  Existing work on updating relational views can then be leveraged to determine whether or not the relational
views are updatable with respect to the relational updates, and if so, to translate the updates to the underlying
relational database. In particular, we demonstrate how to use an approach by Dayal and Bernstein, which determines
the updatability of a relational view using key and foreign key constraints. The expressiveness of XML views allowed
by query trees is evaluated both in terms of the limitations of query trees with respect to languages such as XQuery,
as well as their ability to capture XML views in practice.