According to ERA RINF recommendation 013REC1047: "XXXXXXXoperational pointXXXXXXXX(OP) means any location for train service operations, where train services may begin and end or change route and where passenger or freight services may be provided; XXXXXXXoperational pointXXXXXXXX means also any location at boundaries between Member States or infrastructure managers." This is an overarching concept that could become a union class in an OWL ontology, but cannot be used in the present conceptual model (polysemic term that would induce multiple inheritance issues). It is provided here as an abstract class, in order to make lookup possible, but instantiation impossible.