The atg.commerce.pricing.GroupDiscountCalculator, which extends the DiscountCalculatorService, is located at /atg/commerce/pricing/calculators/
GroupDiscountCalculator. The calculator is responsible for calculating the discount for a group of items.

Items that are discounted together as a group are identified by a group ID property, targetSetID, which the discount calculator uses to link items when obtaining the item discount. The targetSetID is also added to pricing adjustments that are created for any detailed item price information that gets discounted.

To use this calculator, set the calculatorTypeCalculators property of the ItemPricingEngine to grpDiscount.