Billing Class – usually it represents the customer class: residential, industrial, commercial, wholesale
Rate Category – represents the product that is sold to the customer
Rate – represents a unit of variant programs associated with a charge. For example if you calculate the energy charge for 4 products is better to create only one rate and use it for all 4 products
Schema: it contains the collection of the rates. Best practice is to have one schema for one rate category. This is better for readability of the schema.
Everything is linked in Is-u billing. At the Installation you have the rate category.
At the Device you have Rate type. Rate Determination is done based on Rate Category and Rate type. Rates have steps which calculate the Amount based on price keys and consumption. Multiple rates are included in a Billing Schema. Each Rate category is assigned to a billing schema.
Rate type can also be assigned at device, facts etc level. Rate type is another attribute for identification of Rate apart from rate category. A simple case is to determine rates using rate type assigned at register level.
Other cases can be – device rate type for device rental rate determination- Rate category Fact rate type to calculate some charges for all the customers belonging to a particular rate category having that rate type – Rate type can also be maintained at installation fact.