I found ingres website but no mention of a database system so I though they were something else that had taken on the name.......
The website seams to suggest a RAD development tool and middleware and use other databases underneath.
In short the current Ingres is related to Postgresql like Xorg is related to XFree86 or Ubuntu to Debian but much much much older.
Wikipeadia also suggests a similar relationship between Posrgresql and SQL Server!
I guess this is one of the benifits of the BSD License.
Peter.