RailML distinguishes "operational" and "commercial" trains. The commercial ones usually correspond to the direct compounds from FBS. When exporting, you can decide how to set the railML attribute name of the direct connections. One can imagine the column header above a column in a customer's timetable (course book): Apparently the train number is displayed above each column. The problem is however in the detail, and for this reason, for the sake of clarity, we have compiled this detail information in the document Labeling of direct connections von Direktverbindungen (PDF, 0,2 MB).