# What value does segment add to BDM? (1-1)

Morten Franorge
Ranch Hand
Posts: 137
I have travel agent in my family that tells me that a segment is much the same as a order line. The value that a segment adds is that it's associating the flight to the itinerary.

Order - Order line - Product
Itineray - Segment - Flight

This makes sense, except that the BDM states that a Flight can only be associated with one Segment. Which means once one "order" for a "product" has been made, no one else can order that "product".

If there is a 1 - 1 relationship, what value is the segment adding? I would have no problem understanding the (Segment *-1 Flight).

Eric Kerry
Greenhorn
Posts: 4
I'm considering the following similarity. What do you think?

Order(1) ----- (1..*)Order line(*) -- (1)Product
Itinerary(1) - (1..*)Segment()(*) --- (1)Seat in Flight

Cleuton Sampaio
Ranch Hand
Posts: 181
IMO you are right to compare Order with Itinerary and Segment with OrderLine.

I have been working with flight reservation applications for a long time and they are very different from the assignment... For example, what happens if the Customer wants to buy two tickets? Have you considered that?

Cleuton (Brazil)

Morten Franorge
Ranch Hand
Posts: 137
From my understanding of the reservation use case, it is possible to do a reservation for 2 seats. I have toyed with this idea:
Itiniary - Segment - Flight - Equipment - Seats
Where the selected seat(s) is a list in segment. While the list of seats in equipment is the number of available seat (and seating classes) for that flight (these seats will not be marked as "taken", they just state the "lay out" of the equipment)

Adrian Irons
Greenhorn
Posts: 14
I think you are right in all your assuptions and I think that is a must to modify the cardinality when you extends the BDOM (segment 0..* - 1 flight ). If you assume that the segment - flight cardinality is 1..1 then you are saying "I flight only exists when a segment exists", in other words "A product exists only when an orderline exists".