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.
42. The system of claim 28 wherein the sellable units are priceable units and the priceable-units are represented as a set of priceable-unit-labels linked to priceable-unit-cores, where a priceable-unit-label is a factored representation of faring-atom combinations and a priceable-unit-core is a factored representation of fare combinations to encode the context-free grammar.