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History Browsing in OLAP and LastNonEmptyLeaf

One of the basic requirements of a modern BI system or Data Warehouse is to be non-volatile, meaning that the DWH will save the history. In this post I'll explain how to implement it in the DWH while assuming that the history can be changed and (the more interesting part) how to implement it in Analysis Services.

Before starting with history saving in the DWH, I need to say that this has nothing to do with Slowly Changing Dimensions. You can work with Type 1, 2 or 3. All you need to take care of is that the fact table will be consistent with the dimension tables. Assuming that the history can change (this is the scenario in my organization), we need to extract all the fact data every time. If you work with staging level/environment/layer you can use it to calculate which records has been changed or inserted and only upsert them to the DWH itself (it's more secure). In our case, we'll work without such staging level so we need to load all the fact data in every load to the DWH.



Tags: design, mdx


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