'An ItemFlow .. may constrain the item exchange between blocks, block usages, or flow ports as specified by their flow properties. For example, a pump connected to a tank: the pump has an “out” flow property of type Liquid and the tank has an “in” FlowProperty of type Liquid. To signify that only water flows between the pump and the tank, we can specify an ItemFlow of type Water on the connector.'

'.. In addition, if there is an item property (corresponds to the conveyed classifier), then one can label the item flow with the item property. For example, a label of “liquid: Water” would imply that the item flow relays Water and this relay is associated with an item property “liquid” of the item flow, i.e., the “liquid” item property is set once Water is relayed.'