DW write transaction system

I have this problem.
• My user executes a report and after with this report the user produces an Excel file. The input is our DW.
• With the report the user updates some information in our transactional system (by a form, line by line).
• The user asks for a new program that, in the same time, produces the Excel file and updates the transactional system.

I have to write an answer to explain why I want change the process and re-write the creation of the Excel file with the transactional system as input and in the same time, in the same program to update the system.
This solution is more expensive, because the DW query is easy to read and if I change totally the input is a long job.
I know that the good practice of BI doesn’t want that the informational system write a transactional system, but my users want to know why. At the long time my solution is more clean and flexible, but I don’t be able to explain why.

Where can I find this information in simple words?

Thanks

I know that the good practice of BI doesn’t want that the informational system write a transactional system, but my users want to know why. At the long time my solution is more clean and flexible, but I don’t be able to explain why.

Actually, having the DW generate information that can be reviewed and fed back into the operational system is a good practice. It is considered a improvement in the maturity level of the overall BI system. This activity is commonly referred to as a 'feedback loop' in the DW architecture.

It is commonly seen in budgeting and planning, as well as marketing and promotion. An easily visible example is Amazon.com's "people who bought this also purchased..." recommendations on their web site.

The data warehouse is used as the source for the same reason the data warehouse was created in the first place... to off-load analysis and large queries from the operational system. It also gives the business a easy way to adjust what they want to generate back to the operational system.

It is important, however, that you construct the feedback loop so that it does not circumvent any safeguards built into the operational system. If you are working with a COTS system, they usually have API's and transactional interfaces through which you pass data. If its a home-grown system, make sure you maintain some audit trail as to how the data got into the system.