Services for Product Category hierarchies

[Jonathon -- Improov]

Is there a service for retrieving all the child categories belonging to a parent category? Is the 
related entity ProductCategoryRollup? This entity seems to allow a child category to have more 
than 1 parent category.

What about field ProductCategory.primaryParentCategoryId?
I see services "createProductCategory" (and update) used to create the necessary 
ProductCategoryRollup record, but not anymore. Same for service "updateProduct".

Do I use the CategoryWorker.java?

Jonathon