Query rewriting in relational databases is by now rather well investigated.
However, in the framework of semistructured data the problem of rewriting has received much less attention. In this paper we focus on extracting as much information as possible from algebraic rewritings for the purpose of optimizing regular path queries. However, there is always information available in the views, even if this information is only partial. Doc 453 Foundations of Databases - Abiteboul, Hull et al. The Lorel Query Language for Semistructured Data - Abiteboul, Quass et al.