need to read, understand, combine, and finally apply them. But when
big amounts of data are treated for automatic extraction by means of
specialized software, being compliant with those policies becomes
very difficult. The problem of applying these policies to the collection
and subsequent use of web-based data is further complicated
by the fact that top-down policies (provided by data publishers) also
need to be integrated by additional (bottom-up) constraints, provided
by data collectors.