Step-3: Not recording Facts

• Transactional fact tables don’t have records for events that don’t occur
  • Example:  No records(rows) for products that were not sold.

• This has both advantage and disadvantage.
  • Advantage: 
    • Benefit of sparsity of data
    • Significantly less data to store for “rare” events

• Disadvantage:  Lack of information
• Example:  What products on promotion were not sold?

Fact tables usually don’t records events that don’t happen, such as items that were not sold. The advantage of this approach is getting around the problem of sparsity. Recall that when we discussed MOLAP, we discussed the sales of different items not occurring in different geographies and in different time frames, resulting in sparse cubes. If however this data is not recorded, then significantly less data will be required to be stored. But what if, from the point of view of decision making, such data has to be retrieved, how to retrieve data corresponding to those items? To find such items, additional queries will be required to check the current item balance with the item balance when the items where (say) brought into the store. So the biggest disadvantage of this approach is key data is not recorded.

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