Advanced mode
All communication with the Mapper Server is done through REST Services. For example, when you save a mapping to the server, that is to the mapper database, the mapping is sent to the Mapper Server through REST Service calls. The Mapper Server then saves the mapping to the mapper database. When you publish a mapping, it is automatically saved to the server and then published, using only REST Service calls.
If you need to communicate with an older mapper database or Mapper Server you can enable the Advanced Mode. You will then be able to use the old way of communicating directly with the mapper database, using JDBC. Advanced Mode is only intended for advanced users and should only be enabled when needed, for example when migrating mappings from an old EC installation.
You should not set up a database connection for the current EC installation. This should only be set up for older EC installations, if needed.