|A conformed hierarchy is one that is shared among two or more fact schemata in a data mart or in different data marts.|
Creating conformed hierarchies is a powerful way of ensuring that information stored in different facts can be consistently integrated. In particular, conformed hierarchies have a primary role in data mart bus architectures because they enable an enterprise view of the data warehouse to be logically achieved even if the different data marts are separately designed and built.
When a conformed hierarchy is added to a fact schema, a new occurrence is created. All the changes made to the conformed hierarchy (in terms of both structure and glossary) are automatically propagated to all the occurrences in each fact schema. On the other hand, changes made on an occurrence of a conformed hierarchy may cause conformity to be lost.
Changes made to a conformed hierarchy won't be propagated if a local override has been performed.
Example, given project with:
- a conformed hierarchy "CH" containing an attribute named "day of week";
- a fact schema "FS" that references "CH".
When renaming "day of week" attribute in "CH", the corresponding one will be renamed in "FS" only if its name has not been previously overriden.