well, if you are looking at what items the department has worked on, then there should be a table or something that denotes who worked on what...that can be you relation.
subreports can be hyperlinks, but usually they just 'appear' as part of the report. A subreport is basically a report inside of another report and is usually linked in some way...it might be as loose as a date range to show work that occurred inside of the given range. They don't have to use the same fields or layouts. They can impact performance as each line that subreport is on will hit the database again. The standard example is if you 100 lines of detail, and each line has a subreport, the report will hit the database 101 times, but in this case it would appear to be twice, which isn't too bad.
The assigned to: value can be the link as long as the values are consistent across the tables.
HTH