Starting at the top of your Pairings bid group, the N-PBS Scheduler reads each of your bid preferences and remembers all restrictions you specify. The N-PBS Scheduler must honor all Set Condition, Prefer Off, and Avoid Pairings bid preference 100% unless you later instruct the N-PBS Scheduler to Forget a bid preference, or the N-PBS Scheduler enters Denial Mode.
When the N-PBS Scheduler reaches your first Award Pairings bid preference, it searches the pool of available pairings (now restricted by any prior Prefer Off and Avoid Pairings bid preferences) and begins awarding pairings that match this preference. Each attempt to place a pairing in your block has a rules check performed against it, to ensure that the resulting block is legal. If the N-PBS Scheduler has awarded as many pairings that match this Award preference as possible and your block is not complete, it moves on to the next preference. The N-PBS Scheduler continues to read your bid until it completes your block or reaches the last bid preference.
If your block is still not complete when the N-PBS Scheduler reaches your last bid preference, it reads the system-generated bid preference, Award Pairings, and begins to fill your block by awarding any available pairings that respect your Prefer Off and Avoid Pairings bid preferences.
If the block is still not complete, the N-PBS Scheduler tries to replace pairings with alternatives that match the same or lower bid preferences and still honor your Set Condition, Prefer Off, and Avoid Pairings bid preferences. For example, the N-PBS Scheduler may remove one pairing that matches bid preference 6 and replace it with two pairings that match bid preference 7 and complete the block.
Also note that shuffling tries create a complete block by replacing pairings that match a higher bid with pairings that have more credit value. Shuffling is the only time when pairings that match a lower bid may be awarded instead of pairings that match a higher bid.
If shuffling does not produce a complete block, the N-PBS Scheduler enters Denial Mode. In Denial Mode, the N-PBS Scheduler deletes your Set Condition, Prefer Off, and Avoid Pairings bid preferences one at a time, starting with the lowest deniable bid preference. After each deniable bid preference is deleted, the N-PBS Scheduler clears your block and goes back to the top of your bid, and starts processing each bid preference again. The N-PBS Scheduler continues to delete deniable bid preferences and reprocess your bid until your block is at the minimum credit window.
Denial Mode handles deniable bid preferences differently from each other.
■ Set Condition and Avoid Pairings bid preferences are removed completely, even if you have more than one option on the bid preference, such as Landings In YWG, YYZ.
■ Prefer Off bid preference options are removed one at a time if you have more than one option on the bid preference, such as a list of preferred days off. In this case, Denial Mode removes the date at the end of the list first, and works towards the left if it needs to delete additional days or dates.
If your administrator sets a target credit value, the N-PBS Scheduler tries to get every block above the target. However, as long as your block is above the minimum credit window, the N-PBS Scheduler does not go into Denial Mode to force your block above the target credit value.
If Denial Mode has removed all deniable bid preferences without producing a complete block, the N-PBS Scheduler tries to create a block using only the Award bid preferences. If the N-PBS Scheduler still can’t create a block, it makes a final attempt using only the system-generated Award Pairings bid preference. This final attempt, called secondary line generation (SLG), ignores all preferences and performs an exhaustive search to find you a complete block. If you don’t have any deniable bid preferences, Denial Mode goes directly to the final completion attempt and attempts to find you a complete block using SLG.