Additve: A masure can participate arithmatic calulatons using all or any demensions.
Ex: Sales profit
Semi additive: A masure can participate arithmatic calulatons using some demensions.
Ex: Sales amount
Non Additve:A masure can't participate arithmatic calulatons using demensions.
A fact may be measure, metric or a dollar value. Measure and metric are non additive facts.
Dollar value is additive fact. If we want to find out the amount for a particular place for a particular period of time, we can add the dollar amounts and come up with the total amount.
A non additive fact, for eg measure height(s) for 'citizens by geographical location' , when we rollup 'city' data to 'state' level data we should not add heights of the citizens rather we may want to use it to derive 'count'
Data staging is actually a collection of processes used to prepare source system data for loading a data warehouse. Staging includes the following steps:
Source data extraction, Data transformation (restructuring),
Data transformation (data cleansing, value transformations),
Surrogate key assignments
A data warehouse can be thought of as a three-tier system in which a middle system provides usable data in a secure way to end users. On either side of this middle system are the end users and the back-end data stores.
One foolproof method is to maintain a field called 'Last Extraction Date' and then impose a condition in the code saying 'current_extraction_date > last_extraction_date'.