How to setup data validation mechanism

Question

Hi, gurus,
Now our customer wants to do data cleansing before loading data into infocube or ods, the source system includes R/3, flat file, and some legacy systems. However the client wants to create a staging area to keep incoming data, and develop some programming to check data validation. The specific requirement is as following:
1. Provider a user interface to let biz man to correct the error record;
2. can code logic to check the data rejection reason, such as field type is wrong, master data doesn't exist, and etc, and can prompt these reason message to assist business guy correct;
They want to create a specific staging for data cleansing purpose, and because refer to my prior experience with some ETL tools, we can ask developer to write embeded program in informatica or datastage to check data quality and write down the rejection reason in a file to assist business man correct;
so if we want to use SAP BW PSA for this purpose, is it feasible? Can we modify PSA to add one column, 'rejection reason' and add some ABAP program here; or you guys have some other good options for this function.
and can we use PSA to keep all data for 5 years? because the annual delta data is not very big, just 4G.
Someone suggests to create Z table in BW system for staging purpose, however this solution can not use BW ETL tool to load data but need heavy ABAP programming, so any good solution on this?
BTW: can I modify PSA structure to add 1 or 2 column, such as reject reason?
and how to use abap program to access Characteristics master data? are there any function module to read master data directly rather than select data from P table or T table?
Regards, ls

Answer 1

I think if the business guy is given some basic BW training and some aspects about correcting PSA records or adding or loading missing master data,then it can work.
The BW monitor does give you good enough messages about the data load errors.
I do not think it is good to modify the PSA..because this is against purpose of having PSA.PSA has records in transfer structure format,as sent by source system.
PSA is often preserved for data reloads that might be needed some point in future.
As u r saying that annual record load is not big,u can preserve PSA and then later develop a custom program to delete PSA's older than..say 2-3 years..(there might a std program for this).
Modifying or adding columns to PSA is not general practice.
For reading master data maybe u can use this fn module..RSAU_READ_MASTER_DATA.