Cataloged Database
Before a client application can access a remote database, the database must be cataloged on the server node and on any client nodes that will connect to it.
When you create a database, it is automatically cataloged on the server with the Database alias (Database_alias) and adopts the Database name (Database_name) in the process.
The information in the database directory, along with the information in the node directory, is used on the client to establish a connection to the remote database.