What Is a Backward-Infeasible Job in Scheduling?

A backward-infeasible job is a new just-in-time order whose backward pass could not fit all its steps between its earliest possible start and its due-date deadline, so the engine rolls the whole job back, forward-schedules it from the earliest start to produce the soonest achievable plan, and flags it for the planner. It is the honest answer to an impossible promise: "you asked to finish by Thursday, but only 16 working hours exist before then, so here is the earliest plan instead."

This entry is part of the EDGEBIC by User Solutions glossary; the broader dictionary lives in the manufacturing glossary.

When a Just-in-Time Plan Cannot Fit

Backward scheduling right-aligns a new job so it finishes just in time against its due anchor, with slack sitting deliberately in front. That works only when enough working time exists between the job's earliest possible start (its floor) and that deadline.

Sometimes it does not. A rush order lands with a deadline so close that the job's total work simply will not fit before it, even starting as early as possible. Right-aligning the steps against the deadline would push earlier operations into the past, which is meaningless. The plan has to do something sensible instead of failing.

How the Fallback Works

The contract is simple: backward scheduling never throws an error where forward scheduling would have succeeded. So when the backward pass cannot fit the job, the engine performs a whole-order rollback. It discards the failed backward attempt for that job and forward-schedules the entire job from its floor, producing the soonest achievable finish.

The fallback is contained to the one job. The rest of the schedule is untouched, and the run still produces a complete, valid plan. The infeasible job is recorded so it can be reviewed, because a forward plan that finishes after the due date is a real signal: this order cannot meet its requested date, and the planner needs to know.

What the Planner Sees

Two site policies govern what happens next.

• Under the default policy, the forward fallback is persisted silently and the job is still recorded as backward-infeasible for later review, so the plan is honest even without interrupting the run.
• Under the alternative policy, the whole scheduling run is held unpersisted and a doesn't-fit popup appears, offering three choices: accept the forward plan, adjust the dates and rerun, or cancel. Nothing commits until the planner decides.

Either way, an impossible due date is never buried. It is either flagged in the background or raised for an explicit decision.

A Concrete Example

A new order needs 24 hours of work and is flagged to finish just in time by Thursday. Only 16 working hours exist between the earliest start and Thursday's deadline.

The backward pass tries to right-align the 24 hours against Thursday, cannot fit them in 16 hours, and rolls the whole job back. It then forward-schedules the job from the earliest start, producing a plan that finishes as soon as physically possible, which lands after Thursday. The job is recorded as backward-infeasible. If the site is set to show the popup, the planner sees the doesn't-fit dialog and can accept the late-but-earliest plan, change the dates and rerun, or cancel the order. If not, the earliest plan is accepted and the job is flagged for review.

How EDGEBIC Uses It

In EDGEBIC, a backward-infeasible job is a new backward-direction order whose backward pass failed and was forward-scheduled instead. The event is recorded on the engine and surfaced to the planner. The governing site policy decides between silently accepting the forward fallback and holding the run to show the doesn't-fit popup, and that policy is read fresh on every run, so changing it needs no restart.

Backward scheduling applies only to new jobs with a real due date; an already-started job reschedules forward from its resume point rather than being right-aligned again. For the full mechanism, the direction precedence rules, and what the lead-time tail on the Gantt means, see the backward scheduling overview and how TOC buffers and direction precedence interact.