  With the emergence of XML as de facto format for storing and exchanging
information over the Internet, the search for ever more innovative and
effective techniques for their querying is a major and current concern of the
XML database community. Several studies carried out to help solve this problem
are mostly oriented towards the evaluation of so-called exact queries which,
unfortunately, are likely (especially in the case of semi-structured documents)
to yield abundant results (in the case of vague queries) or empty results (in
the case of very precise queries). From the observation that users who make
requests are not necessarily interested in all possible solutions, but rather
in those that are closest to their needs, an important field of research has
been opened on the evaluation of preferences queries. In this paper, we propose
an approach for the evaluation of such queries, in case the preferences concern
the structure of the document. The solution investigated revolves around the
proposal of an evaluation plan in three phases: rewriting-evaluation-merge. The
rewriting phase makes it possible to obtain, from a partitioning
-transformation operation of the initial query, a hierarchical set of
preferences path queries which are holistically evaluated in the second phase
by an instrumented version of the algorithm TwigStack. The merge phase is the
synthesis of the best results.
