8. The method of claim 1 wherein the sellable units are priceable units, and the method further comprises: extending, by the one or more computers, the non-terminal nodes of the context-free grammar by the one or more computers providing sets of partially completed priceable units to account for crossed priceable-units.
1. A computer implemented method of pricing a sequence of transportation units, the method comprising: receiving, by one or more computers, a set of sellable-units, each sellable unit comprising one or more flight segments and at least one fare associated with the one or more flight segments; expanding, by one or more computers, the set of sellable units into components; identifying the components that include a crossed combination of priceable units such that a first flight associated with a first priceable unit departs prior to a first flight associated with a second priceable unit, and the first flight associated with the second priceable unit departs prior to completion of a last flight associated with the first priceable unit; translating, by one or more computers, the components of the expanded set of sellable-units that do not include a crossed combination of priceable units into a context-free grammar that is stored on a computer readable medium, the context free grammar representing combinations of the sellable-units; producing, by one or more computers, a parse tree that corresponds to combinations of sellable-units; parsing, by one or more computers, the parse tree to enumerate sequences of flights segments and a fare used with the flight segments to identify a set of sellable units; and combining one or more of the enumerated sequences of flight segments and fares according to the parsing to produce one or more tickets.