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Can you help me understand this sentence about Maser data/routine?

Answers: Have 4 answers
I read the following statement from this forum:
“… if u add an attribute to master data and that field is not getting populated from source system and you want to get it populated dynamically we can write look up code in routine such as getting data from some other master data table.”
1. Can you clarify what this sentence really mean? Any examples?
2. Why is it that in some cases when you modify master data, you don’t have to write a routine to populate it with data but in some cases you do?
e.g. in the quote it says, if the attribute is not getting populated, why will it in some cases and others not?
3. Please explain in particular “..to get it populated dynamically we can write look up code in routine..”
4. Any hints on writing a look up code? Any example?
The best answer: Hi Amanda,
I would understand the sentence you stated as related to load of TRANSACTION DATA (not populating the MASTER DATA) -- and aTripple k example (a good one) shows me that s/he treat it similarly.
When you are retreiving a lot of data from the transaction system (R/3) you may really not getting values of some infoobjects. However, if the infoobject is an attribute of another infoobject which value we have in incoming data, we may get the value of the attribute from master data of main (basic) infoobject. For this you either may use the mentioned functional module (must be accessable through SE37 t-code) or write a lookup routine.
Here (in the text itself and in the threads linked):
Re: Look up at master data in  update routine 
you may see examples of lookup routine and usage of that FM RSAU_READ_MASTER_DATA.
Hope this helps.