Merging results with Skolem functions

ID values can be used to guide the grouping of data:

  WHERE <$> <author> <firstname> $fn </> 
                     <lastname> $ln </> 
            </>
            <title> $t </> 
        </> IN "www.a.b.c/bib.xml"
  CONSTRUCT <person ID=PersonID($fn, $ln)> 
                <firstname ID=FirstnameID($fn, $ln)> $fn </> 
                <lastname ID=LastnameID($fn, $ln)> $ln </> 
                <publicationtitle> $t </> 
            </>

PersonID($fn,$ln) creates a unique ID for each combination.
the PersonID identifier creates a "namespace".
in the result, elements with the same ID are merged.
merging constructs the union of content elements (duplicates are removed).

All person elements with the same ID have their contents merged. (In general, this corresponds to unbounded nesting of queries.)