4. The method of claim 2 wherein the sellable units are priceable units, the method further comprising using faring-atoms to represent sets of flights, and adding a context-free grammar rule further comprises: adding a rule for each faring-atom FA[k] of length L[k] as: FA[k]==>Flight[k][1] . . . Flight[k][L[k]], wherein the symbol “==>” denotes producing.
4. The method of claim 2 wherein the sellable units are priceable units, the method further comprising using faring-atoms to represent sets of flights, and adding a context-free grammar rule further comprises: adding a rule for each faring-atom FA[k] of length L[k] as: FA[k]==>Flight[k][1] . . . Flight[k][L[k]], wherein the symbol “==>” denotes producing. 5. The method of claim 4 wherein the set of sellable units are priceable units and the set of priceable units has priceable-unit-label Q[i], which has a set of possible faring-atoms FAS [i][1]. . . FAS[i][n[i]] for each of its n[i] parts, with individual faring- atoms indexed FA[i][j][1]. . .FA[i][j][m[i,j]] where m[i,j] is the number of faring-atom possibilities for the j′th fare-component of priceable-unit-label i, and the altered grammar is of the form: Ticket ==>S S ==>Q S I <empty> Q ==>Q[1]I Q[2] I . . . I Q[N] (1 fare-component) Q[i]==>FAS[i][1] (2 fare-component) Q[i]==>FAS[i][1] FAS[i][2] (3 fare-component) Q[i]==>FAS[i][1] FAS[i][2] FAS[i][3] (4 fare-component) Q[i]==>FAS[i][1] FAS[i][2] FAS[i][3] FAS[i][4] FAS[i][j]==>FA[i][j][1] I FA[i][j][2] I . . . I FA[i][j][m], wherein S, Q are priceable units and the symbol “I ” denotes an OR operation.