Differing definitions

I've had a varied but extensive history of dealing with government data in
electronic form.  This started as a government documents librarian helping
people find government data in electronic form, continued with sharing it on
the early Internet, and most recently managing government data as a
government employee.  Throughout this experience one of the major concerns
associated with expanding electronic access to government data from multiple
sources has been getting people to recognize and take into account the
differences in the definitions associated with data elements.  This is
particularly important for historical analysis or comparison of multiple
governmental units.  For example, two governments will define unemployment
differently and the same government will change its definition over time.
 Unfortunately, it has been my experience that when people want to do such
longitudinal or multi-government analyses they were often not motivated to
pay attention to these differences.

My question for this list is whether there are any model projects which are
effectively using semantic technologies not just to make data open, but also
to make the related definitional data more visible and easier to understand
or compare across data sources.  It is my hope that the technologies
associated with linked open data can make this type of information more
useful than when it was buried in the back of government documents.

Thanks in advance for any pointers to such efforts.

David Barber