For the purposes of illustration, this screen is divided into three sections. Section 1 contains the name of the stability rule profile and a description of its function. Each stability rule profile has different horizon stability rules assigned to it.

Section 2 contains the different horizon stability rules assigned to the stability rule profile. You can assign the following horizon stability rules to the stability rule profile:

• Stability Rule for Limited Freeze Horizon (Expedite). Apply this rule when a shortage occurs within the limited freeze horizon. DRP uses these settings to determine whether the processed product location is eligible for expediting during this time horizon — that is, whether schedules can be added or increased to resolve the shortage.

• Stability Rule for Limited Freeze Horizon (De-expedite). Apply this rule when scheduled quantities exceed requirements within the limited freeze horizon. DRP uses these settings to determine whether the processed product location is eligible for de-expediting in the limited freeze horizon — that is, how much schedules can be reduced or canceled within this time horizon.

• Stability Rule for Plan Submission Horizon (Expedite). Apply this rule when a shortage occurs within the plan submission horizon. DRP uses these settings to determine whether the processed product location is eligible for expediting during this time horizon.

• Stability Rule for Plan Submission Horizon (De-expedite). Apply this rule when schedule quantities exceed requirements within the plan submission horizon. DRP uses these settings to determine whether the processed product location is eligible for de-expediting within this time horizon.

The pull-down menu and boxes in Section 3 determine how the stability rule profile is configured to do the planning and allow schedule placement. In the next section I discuss the settings to use to determine these profiles.

This pull-down menu offers three options:

• Single Order. This option allows only one expedite in the limited freeze horizon. Multiple de-expedites can occur, but only as full-schedule cancellations. Single-order de-expedites never decrease an existing schedule quantity. Therefore, if a schedule can’t be fully cancelled without causing a shortage, the schedule remains.

• Each Individual Period. This option allows multiple expedites and de-expedites based on the stability rules applied period by period. With each individual period, the de-expediting logic is allowed to either cancel an entire schedule or decrease the quantity of the existing schedule.

• No Change of Order Quantity. This option does not allow changes to the schedule quantities (expedite or de-expedite) in the limited freeze horizon. 

The Schedule Orders According to All Demands (Ltd. Fr. Hor.) check box is considered only if Each Individual Period is selected as the method for order scheduling in the above pull-down menu. If this indicator is set and there is an excess or shortage within the limited freeze horizon, the system replans rounded net demand (constrained) for every period starting with the excess or shortage through the end of the planning horizon without considering stability rules.

When the Plan Submission Horizon: Recheck After First Change box is checked, the plan submission horizon stability rules are applied every time DRP plans.

When the Consider Change Horizon box is checked, DRP makes no schedule changes within the change horizon.

Limited Freeze Horizon (Expedite) Stability Rule

To access the Limited Freeze Horizon (Expedite) stability rule, click the second folder in the dialog structure shown in Figure 1. Click  the row with Seasonal Aggressive rule, as shown in Figure 3. 

Figure 3

Click Seasonal Aggressive to get to the Limited Freeze Horizon (Expedite) stability rule

This takes you to the screen shown in Figure 4. There are four sections in the Limited Freeze Horizon (Expedite) stability rule, as shown in Figure 4.

Figure 4

Horizon Stability Rule Limited Freeze Expedite

Again, for the purposes of illustration, this screen is divided into sections. Section 1, Header Section, contains the Stability Rule for Limited Freeze Horizon (Expedite) profile ID and a brief description of the profile. The Increase Safety Stock Proportion  box controls whether safety stock is prorated from the first period of the planning horizon up to the end of the limited freeze horizon. You use the prorated safety stock to calculate the net requirements and the schedule delivery line quantity. For example, if the user has 10 pieces of safety stock and a 10-day limited freeze, the calculation uses one piece the first day, two pieces the second day, three pieces the third day, and so on. This is valid only for the Each Individual Period method for order scheduling.

Section 2 of Figure 4, Eligibilty Checks, contains figures that you use to determine if there is a need to expedite schedules during the limited freeze horizon. The system calculates total net demand and compares it with the x%, y% , and z parameters for eligibility check.

The first parameter x%, determines if the need is significant enough to expedite during the limited freeze horizon. The value of x is determined by adding the total gross demand of the period being reviewed to the next 20 periods and multiplying this amount by % of x, the amount entered in the x% of the Sum of the Total Gross Demand field in Figure 4.

For example, if the profile says x% = 0.75 and the sum of total gross demand for the current period + the next 20 days = 20, then x = 15 pieces.

The second parameter, y%, reviews z work days and validates if the total net demand is within y. To determine y, add the total gross demand of the period being reviewed to the next 20 periods and multiply the sum by % of y, which is the value entered in the y% of the Sum of the Total Gross Demand field in Figure 4.

The value of z is set by the user in the limited freeze expedite profile. The period being reviewed based on z days equals the current date plus (z-1). If the profile says y% = 0.50 and the sum of total gross demand for the period being reviewed plus the next 20 periods = 20, then y = 10 pieces.

The total net demand of period z equals the projected supply shortage of the previous period in which a shortage occurred, plus all checked requirements in review through period z, minus any receipts through period z. If the total net demand in period z is greater than y, and z days is less than or equal to the end of the limited freeze horizon, then this product is eligible for expediting during this time period.

The specific requirements check boxes can be used to identify which requirements are considered by the Limited freeze horizon  (Expedite) stability rule. For example, if the Use Forecast box is not checked, the forecast is not considered for the net demand calculation.

Section 3 of Figure 4, Schedule Placement Checks, determines the quantity and the period in which the expedited schedule is placed.

The value of w is determined by adding the total gross demand of the period being reviewed to the next 20 periods and multiplying this amount by % of w, the amount entered in the w% of the Sum of the Total Gross Demand field in Figure 4.

For example, if the profile says w% = 0.25 and the sum of total gross demand starting from the period being reviewed + the next 20 periods = 20, then w% = 5 pieces.

Determine the total net demand as described above in the description of Section 2, Eligibility Checks, of Figure 4. When you are using the single-order method of ordering, if the total net demand is greater than or equal to w, place the schedule in that time period for the quantity that equals largest total net demand in the limited freeze horizon. The system carries out this calculation in the background and expedites the quantity. Otherwise, loop time periods until the total net demand is greater than or equal to w.

When you are using the each individual period method of ordering, if the total net demand is greater than or equal to w, place the schedule in that time period for the quantity that equals largest total net demand in the Economic Order Quantity (EOQ) period. Otherwise, loop time periods until the total net demand is greater than or equal to w.

The first period in which total net demand is greater than or equal to w% is when DRP places the schedule. However, it does not use the total net demand calculated for that period. Instead, it uses the largest total net demand in all periods in the limited freeze.

The value of w% should not be set higher than that of x% or y% . If it is, you risk not placing the schedule when the net demand calculation determined it should be.

If a shortage within the limited freeze horizon is eligible for a schedule change, the next step is to determine the date and quantity of the schedule line. The period in which the order is scheduled is not necessarily the same period in which the first shortage was eligible. It might be earlier because if the order is inside the limited freeze horizon, it might as well be ordered early enough to cover an earlier shortage that was not significant enough to qualify for an expedited schedule.

The Use Normal EOQ Period check box and Overridden EOQ Period field are used to determine when the order change is scheduled. If the box is not checked, the system uses the overridden EOQ period entered in the field. If you are not using the single-schedule ordering method, multiple schedules result, which may be undesirable.

The Ign. Non-Fix. D.R. (ignore non-fixed distribution receipts for rounding to EOQ period) box determines whether the system ignores or considers non-fixed distribution receipts for the supplier for rounding to EOQ periods. This means any existing schedule that is not due within the limited freeze horizon or that is not marked fixed is not used during planning.

Section 4 of Figure 4, Additional Buffer Period, contains the check box Max Plan Horizon: Net Dmd Calculation + Order Sched. This check box is used to consider a buffer period over and above the limited freeze horizon for calculating net demand and order scheduling. The value for the buffer period is entered in the Max plan horizon: buffer days after limited freeze hor field. This value is used to limit the period considered for calculations that improve runtime performance.

Total net demand is the sum of the projected stock or supply shortage of the previous period plus all checked requirements of the period in review through the EOQ period, minus any receipts through the EOQ period.

For  example, suppose the period for which total net demand is being calculated has a supply shortage of 100. You would have to go to each location under this entry location and identify what needs to be excluded. If safety stock is not checked in the configuration, then you would have to subtract safety stock for each location to come up with the true supply shortage.

After you determine the true supply shortage, add all the checked requirements for each period in the limited freeze horizon (if your method of ordering is single order) or through one EOQ period (if your method of ordering is each individual period).

If total net demand is greater than or equal to x, proceed with checking the y parameter within z days. If total net demand is not greater than or equal to x, expediting is not done for this product during this time horizon.

To understand the concept of expediting schedules in the limited freeze horizon, consider a

scenario with gross demand for a seasonal product in various periods, and schedules placed to the supplier in the limited freeze horizon  to fulfill this demand. Stability rules are defined and assigned to products according to their attributes. Use transaction code /SAPAPO/MAT1 to assign the stability rule SEASONAL to the product location (Figure 5). 

Figure 5

Stability rule assigned to the product location

The SEASONAL stability rule has the rule LTDFRZSES assigned for expediting in the limited freeze horizon, as shown in Figure 2. You maintain the parameters for the rule LTDFRZSES in customizing, as shown in Figure 6, which is the same screen shown in Figure 4. 

Figure 6

Stability rule for limited freeze horizon (expedite) with various parameters

Parameter x is derived and compared with total net demand before proceeding with further checks. As seen in Figue 6, x% = 5%, and the method of ordering, as indicated in Figure 2, is single order. In our example, the data indicates a shortage on the last day of the freeze horizon. Figure 7 (transaction code /SAPAPO/DRPM) is a mock-up of the DRP matrix displaying the total gross demand, in which the column headings are periods in the limited freeze (LF) horizon and plan submission horizon (PSH). 

Figure 7

Total gross demand in the DRP matrix

The DRP matrix contains various receipts and requirement elements of a product location that are used for the calculation of the net demand. Calculate x by starting in LF1 and adding the next 20 days (scaling factor) of total gross demand. Multiply this number (65) by the % of x indicated in Figure 6 (5 percent), and you get x = 3.25 pieces, meaning there is sufficient need to expedite during the limited freeze horizon if the shortage during this period exceeds 3.25 pieces. 

Figure 8 is a mock-up of the DRP matrix (which can be accessed in the system through transaction code /SAPAPO/SPPDRPM) showing the various key figures that are considered in the calculation of the total net demand through the end of the EOQ period. Some of the columns, such as the Use column that indicates the inclusion of the key figure in the calculation of total net demand, are provided for the better understanding of the concept and are not available in the system. The inclusion or exclusion of a key figure is controlled in the configuration of the stability rule as shown in Figure 6. The steps for calculating the total net demand are as follows.  

Figure 8

A mock-up of the DRP matrix

Add all the backorders, forecast, and fixed demand to calculate the total net demand for the period LF-1 (limited freeze minus one day). Add all the checked requirements from LF 1 (limited freeze day one) until the end of the EOQ period. The backorder is a given and always is added if the stability rule is not set to No Change of Order Quantity

You start with the plan period before the limited freeze, including the backorder, and go through each period up to the EOQ period. Add the the backorder, forecast, and fixed demand numbers for the period from before the limited freeze horizon (LF - 1) until the EOQ period (LF8/EOQ Period), subtracting any receipts received during the period. This leaves you with a total net demand of 10 pieces.

Compare the total net demand with x, which, in our example, is 3.25 pieces. Because the total net demand is greater than x, proceed to derive y within z workdays and determine if the total net demand is eligible to be expedited within the limited freeze horizon.

As shown in Figure 6, y is 8 percent, z is five workdays, and the method of ordering is single order, as indicated in Figure 2. Recall that the data in our example indicates a shortage in the last day of the freeze horizon. Calculate y as follows.

Starting in LF1, add the next 20 days of total gross demand (see Figure 7 for the values), which gives you a sum of 65. Multiply this by the % of y (8 percent, as indicated in Figure 6). This yields a product of 5.2 pieces.

To determine the value of y within z days, the total net demand, from Figure 8, starts at 10 in LF -1 and increases to 15 in LF 1. Stability rules continue to check the requirements until LF 5, because z indicates a period of five days.

At the end of the five-day period indicated by z, the total net demand (30) is still greater than y, (5.2). Because no period within z was able to recover to within y, expediting within the limited freeze horizon  is necessary to prevent shortage, and this product is eligible for schedule placement w% calculation.

To determine the date and quantity to be expedited in the limited freeze horizon, you must calculate w. As shown in Figure 6, w% = 5% and the method of ordering, as seen in Figure 2, is single order.

As when calculating x and y, start with LF1 and add the next 20 days of total gross demand (see Figure 7 for the values). The sum is 65. Multiply this total by the % of w, 5%. You end up with a product of 3.25 to compare with the total net demand.

To derive total net demand, place the expedited schedule for the largest quantity in first period in which the net demand calculation exceeds x% and y%. The safety stock is now part of the calculation for total net demand, as seen in Figure 9, which is a mock-up of the DRP matrix. You can access the DRP matrix using transaction code /SAPAPO/DRPM. 

Figure 9

Key figures in the DRP matrix

Place the expedited schedule in the first period in the limited freeze horizon in which total net demand is greater than w. In this case, LF 1 had a total net demand of 25 pieces, which is greater than w (3.25). Find the largest total net demand quantity in the limited freeze horizon. In this case the period after LF 5 shows a total net demand of 50 pieces. Stability rules use this quantity to place the order. This is reflected in the rounded net demand.

After the schedule is expedited, the system can be configured to generate and send out alerts to suppliers so that they can take action.