OPS.10.1:4.2 - Construct usable service and a first load bound

Use the operating model to identify the resources needed by each activity, including simultaneous needs. Recover usable calendars, capabilities, access, setup, interruption, restart and return rules. An unattended machine interval may occupy the machine while releasing its operator.

For a finite horizon, sum the required remaining occupancy separately for each resource. Compare it with the time in which that resource can perform this work. If the requirement exceeds that time, the proposed completion is impossible under those inputs. If it fits, timing, precedence or resource compatibility may still prevent a schedule.

For recurring demand, a useful first load expression is:

resource demand per unit time =
    sum over arriving classes of
    (class arrival rate * expected resource time used by one arrival)

Expected resource time includes the modeled visits, setups and recovery attributable to that arrival. A return may require another visit without producing another delivered order. If return behavior depends on congestion or policy, recover that dependence before reusing the old expectation.

Divide this demand by the usable resource time supplied per unit time to obtain an offered-load ratio. It can exceed one: the work offered exceeds that capacity. The observed fraction of time busy remains at most one. Both measures can be useful, but they answer different questions.

Define service time for the chosen server. Include an interruption in effective service when the model treats it as extending that server’s service; otherwise represent the unavailable interval separately. Count its loss once. Waiting for another team or for permission is not automatically occupancy of this server. A batch’s shared machine time is also different from the sum of its parts’ elapsed times. OPS.11.1 and OPS.15.1 supply these resource and event constructions.