Within Data Vault there are special entities which leverage the query performance on the way out of the Data Vault. These entities are placed between the Data Vault and the Information Delivery Layer and are necessary for instances in which many joins and aggregations on the Raw Data Vault are executed what cause performance issues. This often happens when designing the virtualized fact tables in the information and data marts. Thus, to produce the required granularity in the fact tables without increasing the query time, Bridge tables come into play. Bridge tables belong to the Business Vault and have the purpose of improving performance, similar in manner to the PIT table which was discussed in a prior newsletter.
As a means to achieve its goals, the bridge table materializes the grain shift that is often required within the information delivery process. Though, before we dig deeper into the specifics of using a bridge table for performance tuning, it is important to first define granularities within a data warehouse.