Database monitor item in 1.8.1

[alixen]

Hi,

I have seen a new item type "Database monitor" but haven't found any documentation.
Additional parameters are:
DSN=<database source name>
user=<user name>
password=<password>
sql=<query>

I suppose that Zabbix server connects directly to remote database. Is it true ?
How to access remote databases (behind firewall) ?
What databases are supported (MySQL, PostgreSQL, ...) ?
Are there any new dependencies on the server ?

Thank you
Alixen