-- application_ports: which ports an application typically uses (many-to-many).
-- port_number is not a strict FK to ports to allow registering an application
-- before its port entry exists in the catalog.
CREATE TABLE IF NOT EXISTS application_ports (
    application_id INTEGER NOT NULL REFERENCES applications(id) ON DELETE CASCADE,
    port_number    INTEGER NOT NULL,
    PRIMARY KEY (application_id, port_number)
);