DimensionalSample
Galaxy schema
Several fact tables sharing conformed dimensions (also called a fact constellation). Different processes can be compared on the same date, product and store.
Try this
- 01Look for the “Conformed” badges: those dimensions are joined by both fact tables.
- 02Ask the sell-through question and read the SQL: each fact is aggregated on its own before the results meet. Joining two facts row to row would double count.
- 03Click dim_customer, then dim_supplier: each belongs to only one process.
Notation
- Fact tables
- One per business process (sales, inventory), each at its own grain.
- Conformed dimension
- A dimension shared by more than one fact with identical keys and labels, so results line up.
- Private dimension
- A dimension only one process needs (customer for sales, supplier for inventory).
- Drill across
- Querying two facts separately at a shared grain, then joining the results on conformed attributes.
Use it when
- Several business processes that must be compared
- An enterprise bus matrix of shared dimensions
- Growing a warehouse one process at a time
Avoid it when
- Teams cannot agree on shared definitions (the dimensions will not really conform)
- Only one process is in scope