private function getDefaultClasses()
    {
        // TODO use constants for keys

        return [
            'address'               => [
                Cart\Model\CartInterface::class   => Cart\Entity\CartAddress::class,
                Order\Model\OrderInterface::class => Order\Entity\OrderAddress::class,
                Quote\Model\QuoteInterface::class => Quote\Entity\QuoteAddress::class,
            ],
            'attachment'            => [
                Cart\Model\CartInterface::class   => Cart\Entity\CartAttachment::class,
                Order\Model\OrderInterface::class => Order\Entity\OrderAttachment::class,
                Quote\Model\QuoteInterface::class => Quote\Entity\QuoteAttachment::class,
            ],
            'notification'          => [
                Cart\Model\CartInterface::class   => Cart\Entity\CartNotification::class,
                Order\Model\OrderInterface::class => Order\Entity\OrderNotification::class,
                Quote\Model\QuoteInterface::class => Quote\Entity\QuoteNotification::class,
            ],
            'item'                  => [
                Cart\Model\CartInterface::class   => Cart\Entity\CartItem::class,
                Order\Model\OrderInterface::class => Order\Entity\OrderItem::class,
                Quote\Model\QuoteInterface::class => Quote\Entity\QuoteItem::class,
            ],
            'adjustment'            => [
                Cart\Model\CartInterface::class   => Cart\Entity\CartAdjustment::class,
                Order\Model\OrderInterface::class => Order\Entity\OrderAdjustment::class,
                Quote\Model\QuoteInterface::class => Quote\Entity\QuoteAdjustment::class,
            ],
            'item_adjustment'       => [
                Cart\Model\CartItemInterface::class   => Cart\Entity\CartItemAdjustment::class,
                Order\Model\OrderItemInterface::class => Order\Entity\OrderItemAdjustment::class,
                Quote\Model\QuoteItemInterface::class => Quote\Entity\QuoteItemAdjustment::class,
            ],
            'item_stock_assignment' => [
                Order\Model\OrderItemInterface::class => Order\Entity\OrderItemStockAssignment::class,
            ],
            'payment'               => [
                Cart\Model\CartInterface::class   => Cart\Entity\CartPayment::class,
                Order\Model\OrderInterface::class => Order\Entity\OrderPayment::class,
                Quote\Model\QuoteInterface::class => Quote\Entity\QuotePayment::class,
            ],
            'shipment'              => [
                Order\Model\OrderInterface::class => Order\Entity\OrderShipment::class,
            ],
            'shipment_item'         => [
                Order\Model\OrderShipmentInterface::class => Order\Entity\OrderShipmentItem::class,
            ],
            'invoice'               => [
                Order\Model\OrderInterface::class => Order\Entity\OrderInvoice::class,
            ],
            'invoice_line'          => [
                Order\Model\OrderInvoiceInterface::class => Order\Entity\OrderInvoiceLine::class,
            ],
        ];
    }