Mastering Data Warehouse Aggregates: Solutions for Star Schema Performance

Glossary

accumulating snapshot

A fact table design that models an item as it undergoes a uniform series of events or milestones. Aggregation of an accumulating snapshot usually destroys a significant portion of its analytic value, removing multiple milestones and eliminating its ability to support lag calculations.

aggregate dimension table

A stored summary of base schema information that contains dimensional attributes. An aggregate dimension table must conform to a base dimension table. Aggregate dimension tables are typically invisible. An aggregate navigator rewrites queries to access aggregate dimension tables as appropriate; the end user need not know they exist.

aggregate fact table

A stored summary of base schema information that contains facts and foreign key references to one or more dimensions and/or aggregate dimensions. An aggregate fact table stores data from a base fact table at a coarser grain. An aggregate fact table may be invisible to end users if it adheres to fundamental principles outlined in Chapter 1. An aggregate navigator hides its presence from end users. Some aggregate fact tables transform the base data in some way; these derived fact tables do not meet the requirements of an invisible aggregate but may provide benefits as additions to the base schema.

aggregate navigator

A component of the data warehouse architecture that rewrites application queries to leverage aggregate tables. The aggregate navigator maintains all information needed to rewrite ...