modelling hierarchical data warehouse dimension - sql

Question

I'm trying to model a dimension that is hierarchical and has an indeterminate amount of features at each level. Here's an example on how the tables are structured in the data source
+-------------+ +-------------+ +-------------+
|Product +--------------+SubCategory +----------------+Category |
+------+------+ +------+------+ +-------+-----+
| | |
| | |
+------+----------+ +-------+-------------+ +-------+----------+
|Product Features | |SubCategory Features | |Category Features |
+-----------------+ +---------------------+ +------------------+
There's a one to many relationship from Product -> SubCategory and from SubCategory -> Category. Each of the Product/SubCategory/Category also reference their respective features table. The number of features is however not fixed and could be 0.
The fact tables I'm trying to build needs to be at the level of product for its grain, and without the features I could just make a dimension with each of these as columns like so:
+-----------------+
|Dim_Product |
+-----------------+
|Dim_Product_Id |
|Product |
|SubCategory |
|Category |
|... |
+-----------------+
But then all the features would be lost.
Is it possible to keep the dimension at the product level and keep all the features from each hierarchy? Or would it be necessary to make a bridge table containing all the combinations of all the features in the hierarchies? Would I need to break the levels out into their own dimension (i.e. Dim_Product, Dim_SubCategory, Dim_Category) instead? There is also fixed attributes for each heirarchy level, so can these be just flattened out and included as columns if a single dimension is a suitable option?

Answer 1

It seems tricky, since you don't know exactly the number of features, this is my suggestion, though the bridge table would be quite big.
+-----------------+
|Dim_Product |
+-----------------+
|Dim_Product_Id |
|Product |
|SubCategory |
|Category |
|... |
+-----------------+
|
|
+-----------------+
|BridgeTable |
+-----------------+
|Dim_Product_Id |
|Feature_Id |
+-----------------+
|
|
+-----------------+
|Features |
+-----------------+
|Feature_Id |
|FeatureDescription
|TypeOfFeature |
+-----------------+
with TypeOfFeature being one of (ProductFeature, SubCategory, Category).