On inbound maps, only one occurrence of a segment is allowed on a single level. On outbound maps multiple copies of a segment are allowed. In other words, segment mapping is single for inbound maps and multiple for outbound maps.
The DTM segment provides an excellent example. On outbound maps, you can specify that two DTM segments for two dates be generated at a particular level, whereas on inbound maps, the mapping of the dates would be dependent on the qualifier in the DTM segment itself.
