OLAP business databases - some technical OLAP issues
6 important questions on OLAP business databases - some technical OLAP issues
- Typically, OLAP cubes have a density of ...%
Why meaningless surrogate keys?
How to deal with changes in dimension attributes?
1. Overwrite old values
2. Add ‘version number’ field as part of the key
3. Add new column(s) to dimension table
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What is overwriting and what are the consequences? Infrequent changes (e.g., new customer address)
= restating
- Kills information: no history
- Use for correction of errors
- Sometimes history is not important...
What is Add ‘version number’ field as part of the key and what are the consequences? Small individual changes (e.g., store size has been enlarged)
- Insert new record with new version number
- Optional: use additional fields like ‘date from’ – ‘date to’
- Time-sliced version of customer/store/...
- Most popular solution
- NO referential integrity anymore, or refer with complete key
What is Add new column(s) to dimension table? Suddenly big changes (e.g., new categorization)
- Save old values in new columns
- New values and old values in table
- Analysis with old columns is still possible
- Eventually, remove added column(s)
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