Private database link creation requires the same user to exist in both the local and the remote databases.

A public database link can be created only by sys.

A database link can be created only between two Oracle databases.

A public database link can be used by a user connected to the local database instance to connect to any schema in the remote database instance.

A database link created in a database allows a connection from that database's instance to the target database's Instance, but not vice versa.