Bidding methodology is not just how crewmembers tell PBS what the most preferred and least preferred pairings or line from his/her point of view, but also impacts how the PBS interprets the preferences and assigns the best legal line.
[Weighted/Pointed Preferences] (Value-Weighted List)
This method asks crewmember to assign different points to the preferences/pairings. A legal line with the most points will be awarded. This method is hard to describe the preferences and the best line being awarded is not necessarily the preferred line. It gives the crewmember the burden to calculate the "points". Some preferences cannot be specified directly by this method, such as "AND" operator between the preferences. (For example, crewmember cannot exclusively bid two-day-pairings AND layover at specific city.)
[Prioritized Preferences] (Rank-Ordered List)
This method asks crewmember to prioritize the preferences by arranging the bids in a sequence. The "AND", "OR", "IF" logics may be assigned between the bids. Crewmember may bid commands such as "award", "ignore", or "restart" among them. It is bidding in the dark and crewmember builds the line without knowing the reality and legality. If no legal line being built after going through all the bids, crewmember may ask the system to ignore the preferences in reverse order. Preferences may be put in multiple sets or groups. If the current set cannot be awarded a legal line, the next set will be used. There is no relationship between the sets. The next set is just used as a backup if previous set fails.
[Accumulated and Prioritized Layers/Pools]
This method groups preferences in layers/pools. PBS will try to award a legal line based on the pairings that meet all the preferences (with AND/OR logic) in the first layer. If there is no legal line awarded, PBS adds the pairings which meet the preferences at the next layer and tries to award again, and so on. In this way, the most preferred pairings will be held and awarded while adding the other less preferred pairings to finish a legal line. Crewmember can also bid to discard existing pairing pools to make them not "accumulated". This method is the easiest and the most comprehensive. It is also possible to view the exact pairings qualified in each layer immediately, so the crewmember can predict his/her chance in the layer being awarded, which also helps crewmember submits preferences correctly.