An external schema is a collection of views on tables. The external schema of a database may reveal partial information about the tables underneath. Think of it as stored queries that only expose information the client is interested in. For instance, a public website that looks up course information might not need all information on a course that the database has, so we might create a view on the Courses table that only exposes relevant information, such as Course ID, faculty, number of seats, number of students registered for the course, etc, and not expose information such as a list of students registered for the course (which only the registrar needs).