On decidability of boundedness property for regular path queries

The paper studies the evaluation of regular path queries on semi-structured data, i.e. path queries of the form nd all objects reachable by path whose labels form a word in p where p is a regular expression. We use local information expressed in the form of path inclusions in the optimization of path queries. These constraints are of the form L v where L is a regular language and v is a word; L v means that the answer to L from a given site is included in the answer to v. We call these inclusions RW-path inclusions. The boundedness problem for regular path queries p with respect to a nite set of path inclusions E is to decide whether the answer to p is included in the answer to a nite path query. We prove that the boundedness problem is decidable for regular path queries w.r.t. a set of RW-path inclusions, extending a result of Abiteboul and Vianu in 1].