text: For example: an item placed in a shopping cart, a ﬁle uploaded to a storage system, or an order 
  
  becoming ready to ship. Events can either carry the state, such as: quantity (qty), item price 
  
  (itemPx), and currency; or simply contain*identiﬁers*needed to look up related information, such as: 
  
  customerId and orderId, as shown in the following example of a NewOrderEvent: 