1. Aggregate Improvement and Lost, shrunken, and collapsed
Aggregate management
References:
Aggregate Improvement and
Lost, shrunken, and collapsed
Aggregates exist for performance reasons
Consider aggregates as a way to speed queries
Indispensable to warehouses, just as indexes are indispensable to OLTP databases.
Use aggregate navigators
Rules of thumb:
Double storage requirement by factor of two to allow for aggregations
Aggregates should be times smaller than source fact/aggregate table
Try to accelerate some queries by 1,000 times
Both by Lawrence Corr
March 2004
Ron McFadyen

2. Dimensions in a aggregate schema can be characterized as one of:
Aggregate management
Dimensions in a aggregate schema can be characterized as one of:
Lost
Shrunken
Collapsed
March 2004
Ron McFadyen

3. Aggregate management Lost dimension
A lost dimension is one that disappears – it is in the base schema, but it does not appear in the aggregate schema
e.g.
March 2004
Ron McFadyen

4. E.g. a month dimension replaces the date dimension
Aggregate management
Shrunken dimension
A shrunken dimension is one where a rollup occurs, or where a dimension is replaced by a higher dimension in a snowflake design
E.g. a month dimension replaces the date dimension
How is this type of dimension materialized?
What should be the name of the Primary Key?
March 2004
Ron McFadyen

5. The collapsed dimension does not exist as a table
Aggregate management
Collapsed dimension
A collapsed dimension does not appear as a dimension in the aggregate, rather one or more of its attributes appear in the aggregate’s fact table
The collapsed dimension does not exist as a table
e.g.
March 2004
Ron McFadyen