  A view with a binding pattern is a parameterised query on a database. Such
views are used, e.g., to model Web services. To answer a query on such views,
one has to orchestrate the views together in execution plans. The goal is
usually to find equivalent rewritings, which deliver precisely the same results
as the query on all databases. However, such rewritings are usually possible
only in the presence of integrity constraints - and not all databases have such
constraints. In this paper, we describe a class of plans that give practical
guarantees about their result even if there are no integrity constraints. We
provide a characterisation of such plans and a complete and correct algorithm
to enumerate them. Finally, we show that our method can find plans on
real-world Web Services.
