detecting SQL system

One of the Java developers in my group asked me today if there was any 
reliable and portable way he could query JDBC to find out what database he 
was connected to, Postgres vs Oracle vs TimesTen vs ???

So, I'm curious, are there any SQL standard methods of doing this?  Is the 
information_schema any part of the standard, i.e. could we

SELECT character_value FROM information.schema.sql_implementation_info
    WHERE implementation_info_name = 'SERVER NAME';

?

Or do we have to poke around at each of these DBMS servers and figure out 
whats unique about them ?