Hi,
For connecting any remote database you need DBSL for target DB in your calling system. For that you need to find and extract Remote DB dbsl in your calling system. If the dbsl is supplied by the vendor for SAP applications then you can connect. If not, then check with vendor directly. As you say it's DB4, i am not sure and you need to check in SAP service market place for the same and then try DBconn connect.
Regards