The definition of maintenance is based on the “combination of all technical, administrative and
management activities of the life cycle of an asset, in order to keep it or return it to a state where it can
perform its required function”[2], where the required function is “the function or combination of functions of
an asset considered as necessary to provide a certain service”[2]. In a general overview, there are three major
types of maintenance: preventive, corrective and improvement [3]. In theoretical terms they are defined as: