Requirements

The System shall sprinkle if the lawn needs water
The System shall sprinkle in the morning no earlier then 6:30 pm
The System shall collect rain data from a weather service e.g. Deutscher Wetter Dienst open data server opendata.dwd.de

Use cases

System context

Weather API alternatives

Open Weather Api

City list: http://bulk.openweathermap.org/sample/city.list.json.gz

Example city Willich

{
    "id": 2808559,
    "name": "Willich",
    "country": "DE",
    "coord": {
      "lon": 6.55,
      "lat": 51.26667
    }
  },

Example weather

{
 "coord":{"lon":6.54,"lat":51.26},
 "weather":[{"id":800,"main":"Clear","description":"clear sky","icon":"01d"}],"base":"stations",
 "main":{"temp":28.84,"pressure":1020,"humidity":37,"temp_min":27,"temp_max":30},"visibility":10000,
 "wind":{"speed":1.5},
 "clouds":{"all":0},"dt":1533138900,
 "sys":{"type":1,"id":4909,"message":0.0046,"country":"DE","sunrise":1533095958,"sunset":1533151198},
 "id":2808559,
 "name":"Willich",
 "cod":200
}