Columbia has one or more professional engineers. An engineer is a professional who applies scientific knowledge and mathematics along with innovative ideas, for solving technical problems. They work on applied sciences, and design structures, technologies, inventions and machines within the limitations of practicality, cost and safety. They act, in essence, as the link between pure sciences and the world of human applications. There are limitations in the usage of the term professional engineer, and one has to write licensing examinations (apart from the actual degree) to be able to legally use the term, as well as be responsible for signing, sealing or stamping technical documentation.