35. The system of claim 28 wherein the sellable units are priceable units, and the instructions further cause the computer system to: extend the non-terminal nodes of the context-free grammar by the computer providing sets of partially completed priceable units to account for crossed priceable-units.
28. A computer system comprising: a processor and one or more memory modules; instructions stored on the one or more memory modules causing the computer system to: receive 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; expand the set of sellable units into components; identify 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; translate the components of the expanded set of sellable-units that do not include a crossed combination of priceable units into a context-free grammar; store the context free grammar in computer storage, the context free grammar representing combinations of the sellable-units; produce a parse tree that corresponds to combinations of sellable-units; parse the parse tree to enumerate sequences of flight segments and a fare used with the flight segments to identify a set of sellable units; and combine one or more of the enumerated sequences of flight segments and fares according to the parsing to produce one or more tickets.