There is no getCategoriesForClass endpoint and so the relationship between a Class and Category can only be identified through a LineItem.  The data model for a ‘lineItem’ includes the ‘sourcedId’ for both the Class and the Category (both of these fields MUST be populated i.e. a LineItem MUST be associated with one Class and one Category).  Therefore, use of the getLineItemsForClass endpoint is used and the response payload is then analysed to retrieve the set of 'sourcedId' for the categories. Note that support for the getLineItemsForClass endpoint is optional for both consumers and providers.