The Oracle document states:
A read/write database instance, which is the default, can process DML and supports direct connections from client applications. In contrast, a read-only database instance can process queries, but does not support modification DML (UPDATE, DELETE, INSERT, and MERGE) or direct client connections.
What is direct client connections? I know I can use sqlplus connect to an Oracle database instance, is this direct client connection? Are there any indirect ways to connect to Oracle?