Tag Archives: Repair

Leading Indicator Forecasting in SPP

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What Is It?

A statistical forecast based on sales history is not the only type of forecast that is used in SPP. Sometimes the forecast needs to be based upon factors other than history such as installed base. For instance in A&D, the forecast can be more accurately executed based on installed base rather than historical sales. Leading indicators is a causal forecasting method. (This could be flight hours, or other equipment utilization numbers. These are also called causal factors, or non-demand factors and are notoriously hard to find in company databases.)

If you have information about the failure rate, you can define that in a coefficient. The system then multiplies this coefficient with the equipment that is on the market and can thus forecast how many service parts you will require in the future. The steps generally are:

  1. Equipment source must be tapped and extracted (equipment BOMs, installed based key figures, equipment master data from the BW)
  2. We then bring this into BW, perform a LI preparation service.


Then we select leading indicator folder.


SAP supplies the following leading indicators

  1. Installed base
  2. Operation time
  3. Number of users

You can also define your own leading indicators in addition to the ones provided by SAP. (You must assign the same leading indicator to all locations of a BOD.)

SPPLFISERVICE for Coefficient Determination

These leading indicators are then assigned to a planning profile. You need to select the SPPLFISERVICE. This service is the coefficient determining service. The system generates the demand histories for the leading indicators used. It then uses these histories to determine a value for the coefficient for each period in the past. To do so, it executes the planning service SPP: Preparation Service for Leading Indicator Based Forecast (SPPLFISERVICE).However, you do not need to run the LFI service. If you select either CONSTANT VALUE or MANUALLY ENTERED off of the Leading Indicator tab of the forecast profile. This leads us to an intermediate topic – the Foreast Profile Leading Indicator Tab. Goto this link to read this related topic. Then return to this post. Alternatively, open both posts and read them side by side.

http://www.scmfocus.com/sapplanning/2008/10/02/spp-leading-indicator-forecast-profile-tab/

Here is the SPPLFISERVICE, it is a standard service and can be accessed by creating a planningprofile and by attaching the service to this profile.


/N/SAPAPO/480000009


The service is in the product simple category.


Now we have selected the correct Process Profile category we can go to the next step and select the SPPLFISERVICE.


Now we can access this service by selecting this Leading planning profile that we just created.

If you use period based planning, SPP generates the forecast for a product either on the basis of past sales values or on the basis of leading indicators. If you can not meet your demand within your BOD, SPP covers demands either through external procurement or repair.

SPPFCSSERVICE for Forecasting

This generates the demand histories and performs forecasting. However, you can use the interactive forecasting screen instead. /N/SAPAPO/SPPFCST

On the other hand you can also tie up this service in a planning profile.


STEPS

  1. Based on the demand history generated in step one, the system generates the forecast for the leading indicator and the coefficient. For this you can either schedule the planning service SPP: Forecast Service (SPP_FCS_SERVICE) which generates the demand histories, or you can start the forecast manually in the interactive forecasting screen. This generates the forecast for the leading indicator. In doing so, it proceeds as specified by you in the Leading Indicator Values field on the Leading Indicator tab page in the forecast profile. You have the following options.

a. Forecasted – In this case the system performs the forecast on the basis of the demand history and takes into account the forecast profile that you have defined for the leading indicator

b. Determined from the Installed Base – In this case the system performs a naive forecast. I reads the values from the demand history from the InfoCube SPP: Installed Base Key Figures (9AIBASKF), and copies the value of the current period as the forecast value for future periods

c. Upload / Manually Entered – In this case you can either enter the forecast values manually in the Interactive Forecasting screen or upload them with a BADI

3. The system determines the leading indicator based forecast for your location product on the basis of the forecast values for the leading indicator and the coefficient. As in step 2, this step is either part of the planning service SPP: Forecast Service (SPP_FCS_SERVICE) or part of the interactive forecast that you can start manually in the Interactive Forecasting screen. To generate the leading indicator forecast for your location product, the system multiplies the forecast values of the leading indicator determined in step 2a by the forecast values of the coefficient determined in step 2b. it does so for each period in the future

4. You can display the calculated forecast values on the Interactive Forecasting screen.

Equipment Data

You can load equipment data into SCM from ECC via BI. In the standard, the system transfers equipment data from ECC into the characteristic 0EQUIPMENT in SAP BI. You must schedule this transfer in SAP BI with an InfoPackage.

Overall Sequence

1. The preparation service for leading indicator based forecasting checks all products of the product selection as to whether they are part of a supersession. If a product is part of a supersession, the preparation service checks whether the supersession is a one to one replacement. It is only in this case that the preparation service takes into account this supersession in leading indicator based forecasting. The preparation service for leading indicator based forecasting of the predecessor and successor product then generates a demand history as described below. The preparation service checks whether you have set the read BOM of LI flag in the service profile for the preparation service.

a. If you have set this flag, the system reads all equipment BOMs for the ERP system and check how often a product occurs in which equipment BOMs

b. If you have not set this flag, the system sets an equipment equal to a product.

2. The preparation service checks whether you have restricted your equipment with a selection in customizing or whether you want to take into account all equipment in leading indicator based forecasting. If you want to restrict the equipment taking into account in leading indicator based forecasting, you can define an equipment selection in Customizing. You can specify the semantics and values or value ranges for these semantics that the system is to take into account or not take into account in the selection.

3. The preparation service determines an entry location for all products of the product selection and checks, which leading indicator group you have assigned to this entry location. The system only performs step 4 for those leading indicators that are included in this leading indicator group.

4. If the installed base leading indicator occurs in your leading indicator group, the preparation service distinguishes between the installed base leading indicator and all other leading indicators as follows.

a. The preparation service determines the demand history of the installed base leading indicator form the information from step 1. To do so it counts how often a product occurs in total in all checked equipment BOMs. If you are not using equipment BOMs and an equipment corresponds to a product, the system only counts the equipment.

b. The preparation service determines the first stockholding locations for the product. To do so, it determines at which location the demand for the equipment occurred. If this location is a stockholding location, it determines this location is the first stockholding location. If this location is not a stockholding location, it goes up in the BOD until it finds a stock holding location and determines this location as the first stockholding location.

Whether a location is a stocked location is set here in the SPP Inv. Planning tab on the product location master.

replenishment-indicator
Here the tab for leading indicator has a number of selections which determine if the leading indicator forecast is to be selected from installed based or are manually entered. The coefficient is then used to adjust your mean time between failure.

Forecast Service Profiles


Now we will discuss the planning service indicator.


For details on the Planning Service Manager goto our post on the topic at….

http://www.scmfocus.com/sapplanning/2008/09/28/spp-planning-service-manager

Just some initial screen shots which will be commented further from the forecast profile.


BADI

To define your own logic of wish to use the ATP check for determining the first stockholding location, you can implement the BADI /SAPAPO/EQUIPFIRSTSTOCK_PREP


Major Functionality in SPP

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Hot Topics

Of the functionality in SPP, these areas seem to be some of the most requested:

  • DRP
  • Deployment
  • Inventory Balancing
  • Buy and Repair

We address each of these areas of SPP in this blog. For those looking for the latests improvements in SPP 7.0, they are listed here:

http://www.scmfocus.com/servicepartsplanning/2009/04/02/how-is-sap-spp-developing-as-of-70/

DRP

Determines the new demands of all locations in the BOD, rounds them and aggregates them along the BOD to the entry location.

http://www.scmfocus.com/sapplanning/2009/04/23/spp-drp-stability-rules-and-the-frozen-horizon/

http://www.scmfocus.com/sapplanning/2009/04/19/spp-drp-special-cases-and-consolidation/

http://www.scmfocus.com/sapplanning/2009/04/23/sppdrp-approval/

DRP is controlled in the Make General Settings for DRP configuration.

Deployment

Deployment is not unique to SPP. SNP also has deployment, which is described here.

http://www.scmfocus.com/sapplanning/2008/10/11/snp-deployment-and-fair-share/

Deployment is the normal or “standard” way of running SPP. SPP has the same concepts of distribution such as Fair Share and Push methods.

  • Fair Share use used when there is a shortage of material (can be allocated a number of different ways – including based upon target stock level and quota arrangements)
  • Push is used when there is an overage of material (push deployment is very similar to Supply Distribution in SNP) (also push can be allocated based upon demand in the system, quota arrangement, and safety stock)

Deployment uses the DRP matrix and decouples DRP planning from deployment planning. http://www.scmfocus.com/sapplanning/2009/04/23/spp-deployment-and-fair-share/

Deployment is triggered by a goods receipt at a parent location (push deployment) or by current demand at the child location (pull deployment)

Deployment is controlled by the SPP Deployment tab on the product location master. Feilds include:

  1. Deployment indicator
  2. Review time
  3. Time Btw. Depl Runs

Deployment can be simulated as well.

Inventory Balancing

Inventory balancing repositions inventory to locations where it has a higherlikelihoodof consumption. This capability is also necessary for finished goods, but SNP has no functionality designedspecificallyfor this. However, it is absolutely critical for service parts because of their low volume. At one client we evaluated the use of SPP Inventory Balancing for finished goods simply because it is only functionality in SCM specifically designed for this task.

Stock transfers are the result.

http://www.scmfocus.com/sapplanning/2009/04/23/inventory-balancing-in-spp/

The formula looks like this:

If inventory savings + warehouse space savings + service benefit – the move cost is greater than a threshold, then a movement is scheduled.

Deployment can be run using the heuristic or the optimizer. However, the output of deployment creates stock transfers.

Buy and Repair

This is something that MCA SPO does very well – making decisions regarding repairing vs. procuring new items.

http://www.scmfocus.com/sapplanning/2009/04/22/spp-operating-parameters-and-repair-vs-buy/


SPP Operating Parameters and Repair vs Buy

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SPP Operating Parameters

Overall, the operating parameters of SPP links the stocks within the bill of distribution (BOD) with the actual demands.

(See this post if you are unfamiliar with the BOD).

http://www.scmfocus.com/sapplanning/2008/09/28/spp-bill-of-distribution-bod/

The logic of SPP is if these demands can not be met within the BOD, SPP attempts to cover these demands either through external procurement or repair. This is different from SNP, because repair is not considered as part of the equation. However, in service parts networks, repairable or unserviceable products are frequently kept in the supply chain that can then be repaired by the company, or sent out for repair.

Repair vs Buy

Repair or buy functionality is well suited to high value service parts which are cheaper to repair than procure. If you activate this functionality the system checks whether enough un-serviceable products can be repaired are available. You can also setup the system to always repair. This decreases the processing time of the SPP planning runs.

A product location can have two statuses.

  1. Serviceable – A location product has the serviceable status if it is either new or has been repaired
  2. Un-serviceable – A location product has the un-serviceable status if it has not yet been repaired but is scheduled for repair

The system does not use any stability rules for serviceable location products in the plan submission horizon and in the limited freeze horizon. You can model subcontracting production, but you must have the subcontractor PPMs or PDS configured in PPDS.

Returns Forecast

This is determined using the requirement forecast of SPP for the location product and multiplies this requirement forecast by your entry in the Percentage of Good Quantity of Returned Products field and by your entry in the % of Good Qty of Repairable Products Field. To make a repair decision, DRP needs to know the repair cost for a location product.

The Problem

However, the issue is that the repair vs. buy functionality only has BADI screens. Notice this screen shot.

This is very strange. Any functionality in SCM always has a configuration area in addition to having related BAdIs. This is the first time I can recall running into a situation where it didn’t.

I have checked the documentation on it, and it is not clear that this functionality works. This is interesting because all of  the major service parts planning vendors (MCA Solutions, Servigistics, Baxter) can do this. Currently the one that does not appear able to is SPP. This is a problem because this is critical functionality in SPP.

__________________________

After posting this article on the SPP LinkedIn Group I received this response from Lars Sondergaard, so I thought I would post it here for everyone to see.

Lars Sondergaard • Hello Shaun,Great initiative starting this LinkedIn Group!We found your blog through searching for SPP specific topics.Now regarding the problem you describe where:„A product location can have two statuses“1. Serviceable2. Un-serviceableWe also were stugling a bit on this part, when we had to do a customer demonstation, but we found out that you need to set up EDQA – Event-Driven Quantity Assignment.Depending on the release that you are working on you can refer to the following notes:Note 1081343 – Unserviceable Stock for “Repair or Buy” (Release 5.1) Note 1081024 – TDL: Make settings in ATP and EDQA for SPP (Release 5.1) – probably the more detailedNote 1334332 – TDL: Make settings in ATP and EDQA for SPP (From Release 7.0) – This contains a BC Set I thinkNote 1440517 – stock posting does not trigger the EDQA executionNote 1421828 – Subcontracting stock is not created for SPP ATP catecoriesNote 1405470 – EDQA: SOBKZ to use in Condition Profile for stock changesNote 1378126 – Field “Activation of Process Cat.” in Customizing not copiedNo Badi‘s neededI hope this information can help you out?Best regards,The Westernacher team

SPP Introduction

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The SPP Footprint

SPP or Service Parts Planning is an interesting APO sub-module. This post will take you through a few of the main features. After you have finished reading it, please move on to other SPP articles on this site that get into much more detail. Some of the major functionality in SPP is described in this post…

http://www.scmfocus.com/sapplanning/2008/05/15/spp/

SPP is essentially a duplicate of the DP-SNP footprints but it has its own folder within the mySAP GUI as you can see below:


This essentially a truncated version of DP and SNP. Here you can see the Administrator Workbench is identical to the workbench in DP.

Product Location Master

Areas which are not duplicated include the master data such as the products and location master, which are setup in the general master data area of SCM. SPP also has its own tabs on the product location master called which are the following:

  • Properties of SPP
  • Packaging Data
  • Storage
  • SPP DRP
  • SPP Deployment
  • SPP Inventory Balancing Surplus

Here is one of the tabs.


You can see important additions such as the Warranty Start and End Date and the Production End Date. You can also set the Retention Period. All of these impact service parts planning.

You can see the extra focus areas are particular to service parts planning:

  • Stocking and destocking (this allows you to exclude parts from planning, these could be obsolete parts)
  • Surplus and obsolescence planning
  • Surplus and obsolescence approval
  • Surplus quantity to be processed manually
  • Modifications of product selection
  • Define retention strategy group

Exclusion Rules

Here you can see the exclusion rules apply per planning version and location. You can create a sophisticated matrix which can control all other planning versions in this on location.


So because service parts come in and out of service more often (and require enhanced supersession functionality). In the Planning Service Manager (towards the bottom). However, you must setup a profile in order to get this to work.

Below is the Surplus Approval screen


Below SPP is a related submodule called Service Maintenance Planning


There are only a few capabilities in this area.

Back to SPP, the Location Exclusion Table and Stocking/Destocking selection allows you to remove parts from planning.

SPP also has simulation functionality. These are the selections.

Critical SPP Features There are three critical areas of SPP that really differentiates it from its footprint cousin of DP and SNP.

  1. Bill of Distribution: “The Bill of Distribution business object is used to predefine the distribution routes for products within Service Parts Planning (SPP). To use the bill of distribution (BOD) two or more distribution planning and execution environments have to be linked. One represents the location data management and the other the SPP environment. In these environments, distribution of products occurs between the locations of the BOD based on projected demands at the locations. The SPP environment retrieves the BOD information from the location data management using the Read Bill of Distribution operation.” – SAP Help

  2. Repair fields on the product master – This controls whether SPP should select an item for a repair (based on the value of unserviceable inventory at a location of course)
  3. Supersession

More detail on the BOM can be found here.

http://www.scmfocus.com/sapplanning/2008/09/28/spp-bill-of-distribution-bod/

More detail on supersession can be found here.

http://www.scmfocus.com/sapplanning/2007/12/13/part-supersession-in-sap/

Simulation

Service parts planning always has a significant focus on simulation. This is because service organizations are always trying to figure out the right trade off between service level and inventory investment.

Here you can see the simulation screen below.


Bill of Distribution

The BOD is main focus of SPP. A BOD is an opaque mechanism for segmenting the products under management. The service parts planning software company called MCA has an identical concept, however, they call it a network. It is simply different cuts of the product database. As with APO, with MCA SPO you can run the model optimizer and view the output just for a specific “network.”

You can create a BOD by navigating to the menu below. This is under application specific master data, not under the main SPP menu item:


After creating one, you can assign products to the BOD


You can also view the assignments, that is which products goto which BODs.






Supersession

The Maintain Interchangeability Group menu item is where supersession is controlled. It is not in the SPP menu path but in the Master Data path.


You can set the different types of Groups, one of which is Supersession Chain.


Here you can see we have setup a Suppersession Chain for the SNAPP GROUP which is superseding the part SNAPPTEAPOT for SNAPPCOFFEEPOT. As soon as this is saved this (and after the location is added) the relationship will be made. This is done by selecting the location tab next to the header tab and entering a valid location.


For more on my SPP offering see this link.

http://www.scmfocus.com/consulting/areas-of-specialty/service-parts-planning/


The Challenges of Capacity Planning in SCM

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Introduction to the Issue

The issue of importance is how constrained based planning is how it is handled in planning.

  1. SAP SCM: The constraint based production planning engine in SCM is called PP/DS
  2. SAP PP: Runs MRP and places loads over work centers and resources. These loads can be viewed in SAP and the capacity leveling workbench can be created (Capacity leveling can also be performed in SNP, but that gets into too much detail for this write up)

For more on work centers see this post:

http://www.scmfocus.com/sapplanning/2008/01/05/work-center/

The Challenge of Constraint Based Planning

Much under-appreciated is how difficult constraint based planning is. The complexity does not come from the mathematics, which is relatively easy solution to engineer, rather the difficulty comes in obtaining the constraint data that represents the reality of the constraints in the factory. There are two basic issues with regards to data:

  • Many companies do not maintain adequate databases on the history of work center and resource capacities or their sequence in order to setup the model correctly
  • Few companies are willing to make the effort to constantly update these constraints as things change on the manufacturing floor. Changes to capacity can include:
    • Labor changes in the factory
    • Work centers and resources taken out commission for scheduled and unscheduled maintenance
    • Capacities reduced due to material shortage

The easiest manufacturing environments to model are stable repetitive manufacturing environments. This is because the lines (work centers and routings) rarely change. The most complex environments to model are process industry and job shops.

Capacity Planning and Constraint Based Planning at One Client

Constraint Based Planning

  • PP/DS is the module within SAP SCM that performs constraint based planning. However, this client is not bringing up PP/DS for (although it does have the license) and does not have another constraint based planning engine.

Capacity Leveling

  • This client is not bringing up SNP.
  • This client is bringing up PP (Production Planning) in ECC. However, at this stage this client is only setting up the work centers related to facility layout. Without a far more detailed view into work centers and resources and capacity capabilities, capacity leveling is not going to be feasible.

The Necessity for Capacity Planning and Constraint Based Planning for Lockheed Service Parts

Spares Manufacturing

The interesting issue is that this client manufactures less than 10% of its parts. It has poor knowledge of the capacities of its suppliers’ manufacturing lines.

Supplier Capacity Leveling (procured parts)

However, suppliers can increase their capacity by receiving funds from this client to add manufacturing lines or tooling. In this way the suppliers for parts do capacity planning for this client. In order to do this they would need either or planned inventory and planned demand from the client. The necessity would be in sharing data with these suppliers. However, this client must be able to actually do something to enable suppliers to increase their capacity (i.e. pay them to add capacity).

Repair Capacity Planning

Repairs can be planned in ECC the same way that manufacturing is (in this case work centers model repair areas rather than manufacturing areas. Repairs capacity is notoriously variable. (Although there is s Capacity Requirements Planning area within Plant Maintenance) So much of the work is “open and inspect.”


Part Supersession in SAP

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Supersession
What is Part Supersession?

Supersession is one of the most important functions in any service parts planning system. Supersession is used to both:

  1. Substitute one part for another part
  2. Obsolesce parts due to engineering changes driven by PLM (Product Lifecycle Management) that need to be replaced by newer versions

The supersession configuration in service parts planning systems allows this to be performed automatically during the planning. In MCA SPO this supersession is handled by configuring whether the part is subject to supersession and the type of supersession (One Way or Two Way that applies). We will use the description of supersession in the MCA Service Parts Optimizer Glossary of Terms:

Supersession in MCA

Used to specify that a Part should be replaced with a different Part (referred to as a Planned Part). Supersession processes are part of the forecasting batch process. They transform demand, population and inventory data to reflect it on the currently planned versions of the Part. Three types of supersession processes are performed on data within SPO: Demand Supersession, Contract Population Supersession and Inventory Supersession – MCA Glossary

Supersession Type

Indicates the type of Supersession applicable to a Part. This value (ONE-WAY or TWO-WAY) is used to determine if inventory of the superseded Part can be used for satisfying demands for the superseding Part. Inventory of TWO-WAY superseded Parts is added to the inventory of their superseding Parts, whereas inventory of ONE-WAY superseded. – MCA Glossary

Supersession in SAP

When an external system that is specialized for service parts planning tells SAP what to do, SAP can simply execute the recommendations made by the external system. However, the question arises what SAP ECC’s capabilities are with supersession.

According to SAP web sources, supersession resides in:

  1. Advanced Planning and Scheduling (in SCM)
  2. Supply Chain Management
  3. Service Parts Management (within SCM)
  4. In ECC

Supersession in SAP SCM/APO

SAP documentation states that its SCM module has supersession capability. However, the SAP Service Parts Planning solution is so lightly installed (as of mid 2007) that it does not well represent the supersession capability on a typical SAP install, specificially SAP ECC. However, outside of SPP, APO has supersession (called substitution or interchangability outside of service parts). The way to arrive at it as of SCM 5.0 is to goto

APO – Master Data – Application-Specific master data – Product and Location Interchangeability – Maintain Interchangeability group

You can apply the substitution here or if you are using CTM, in the CTM profile. (see our sister blog for an explanation of CTM)

http://www.scmfocus.com/sapplanning/2009/05/09/ctm/

This is fairly simple, you can see from the screenshot that we have populated the following information:

  1. The Group Type (supersession chain)
  2. The Group name – SNAPP_GROUP
  3. The Group description
  4. What the supersession is relevant for (for both planning and ATP)
  5. Next set the preceding part and the succeeding part

Finally we save this and we will have just created an Interchangeable Group.

Next I need to assign a location. What this means is we can create supersession relationships that just apply for particular locations but not for others.

We have not been able to verify this, (as we presently lack access to a SCM 2007 aka SCM 5.1 system), however the functionality of supersession – interchangability has been enhanced and is now located at:

Advanced Planning and Optimization (SAP APO) – Service Parts Planning (SPP) – Master Data and General Functions for SPP – Product Interchangeability in SPP

The enhancement relates to the ability to use form fit function classes in addition to product supersession. “That is you can define a product as the leading product for each subgroup of a form fit function class. DRP then consolidates the demands and stock of the location products by adding the demand and stock of the non-leading location products with substitute orders to the demand and stock of the leading location product. – SAP SCM 2007 Release Notes

Supersession in SAP ERP

Within SAP ECC, supersession is approximated by the Material Determination functionality. However, within SCM, SAP states that the rule based Available to Promise check does provide this functionality. In ECC product substitution functionality is called Material Determination (MD). The SAP definition of Material Determination is:

“Material determination enables the automatic substitution of materials in sales documents during sales order processing. For example, during the course of a sales promotion, the system can, during sales order entry, automatically substitute a material that has promotional packaging. A consumer product may have a special wrapper for, for example, the Christmas season. Using material determination, the system substitutes the material only during the specified period. Material determination is used for:

  • Customer-specific product numbers with your own material numbers
  • International Article Numbers (EANs) with your own material numbers
  • Substituting discontinued materials with newer materials” – SAP Help

Interesting features of material determination

  1. MD happens during the sales order process
  2. Sales document types (A&D Contract, Repair Quotation, etc.) can be set for MD

This screen shows the connection settings between the Sales Doc Type and Material Determination

Where Should Supersession be Performed?

Supersession logic can be maintained in both the planning system and the execution system. That is both in MCA and SAP. They can be for different purposes however. A few options are:

  • Planning supersession can be performed in MCA, while execution supersession can be performed in SAP ECC (for sustainment, production supersession is a different matter).
  • Planning supersession can be performed in MCA with no sustainment supersession data maintained in SAP ECC. However inventory planners can still use MCA’s user interface to determine the superseeded part, and then execute the supersession in SAP.

In either case SAP will respect the supersession that is performed in SAP as it would be inherent in the New Buy List that came from MCA. The basic questions are:

  1. Is having the execution supersession available in SAP (allowing automated supersession within SAP ECC) worth the additional effort in configuring MD and in the continual maintenance of this supersession list in SAP?
  2. Is the MD functionality capable of providing similar functionality as comes with MCA? That is, is the substution functionality, which is fairly basic, and which would provide automated supersession worth maintaining instead of looking at the MCA user interface and reading supersession relationships from MCA?

Supersession in SAP Documentation

The document below from SAP is light on details.

sap%e2%80%a6service_parts_management.pdf

The best write up on supersession in SAP that we have seen is at:

http://help.sap.com/saphelp_dimp50/helpdata/EN/f7/a62238b497a552e10000009b38f842/content.htm

sales-document-types-in-material-substitution.jpg