The subject of storing tubular data in the Seabed database is less of storing the actual data regarding the tubular goods and more of storing the composition of the tubular assembly. For example, a drill string is composed of everything from Drill Pipe through a Bottom Hole Assembly (BHA), which is itself an assembly of other tubular goods, and a drill bit.
It may be enough for you to describe a drill string as being composed of drill pipe, a BHA and a drill Bit, but in most cases there is a need to show exactly what the composition of a drill string is right down to the components of a BHA.
In addition to using the Facility_Composition mechanism, the Facility_Connector mechanism is also used to store details of the connectors on the components with the name attribute used to differentiate between the top and bottom connector.