Vendor acct group and number range in the MDC vs MDS

Question

IN MDM 3.0 when a new BP with vendor as role is created via UI in MDS the vendor is created with a generic BP number range in the MDS.  The down stream MDC's all have different vendor account groups with different number ranges assigned in each MDC..  example...
client     type of vend   acct grp      num range
MDC1      purch vendor     com2      1000000-1999999
MDC1      acct vendor      act1      2000000-2999999
MDC2      purch vendor     pur1      2400000-2499999
MDC3      purch vendor     POV1      3599999-3599999
How does MDS know when it distributes the vendor to the MDC's what account group and number range to create the vendor with in the MDC's.  The MDC cannot change all its existing master data that has been created already with the account groups and number ranges becuase field variants have been established.  Where is this mapping contained MDS or XI and how is it done.

Answer 1

The number range in the MDS is determined by the value in the "Grouping" combo-box.  This combo-box is populated by values entered in IMG activity Master Data Objects -> Business Partner -> Business Partner -> Basic Settings -> Number Ranges and Groupings -> Define Groupings and Assign Number Ranges.  Each value must have an associated number range and one of the values must be defined as the standard grouping in case the user doesn't select a grouping.  This is how numbering occurs in the MDS.  Unfortunately you cannot assign more that one grouping to a new BP.
Now, for the MDCs.  When sending a new BP to an MDC, for example an R/3, there must be an external number range setup in the MDS for that MDC and it shouldn't conflict with any number range in that MDC. 
IMG Activity Master Data Exchange -> Central Settings -> ID Mapping -> Make General Settings for ID Mapping allows you to define which number range you want to use for a specific object type in a specific system (e.g. KNA1 (customer) in system R/3_100). 
So far this isn't sufficient for you because you have 2 number ranges for MDC1 in your example. 
In the IMG activity I just mentionned, there is also a possibility to add an additional parameter which allows you to assign a number range for each unique object-type/system/additional parameter combination.  By putting the account group in the additional parameter field, this allows you to assign number ranges per account group.
What remains to be done is to use this information in the XI Mapping for BP to R/3 Vendor.  The first thing is for the XI Mapping to map the MDS account group to the MDC account group.  Then the XI Mapping must call the MDS to create a new ID-Mapping between the BP and the Vendor.  During this call, the XI Mapping must provide all the usual parameters as well as the account group.  This will ensure that the correct number range will be selected so the correct vendor id will be generated.  This id will then be used in the ID Mapping.
If you need to create the Vendor for multiple account groups, then you will have to implement special logic to map the MDS account group from the BP to the many MDC account groups needed for the Vendor.
Hope this helps!