6.5 Use Case: Subscribe to be notified when temperature is above/below threshold in building (UC4)

Use Case 4 (UC4) is subscribing to changes in the indoor temperature of a building, filtering for an indoor temperature greater than 30°C, i.e. only once the threshold of 30°C has been crossed, notifications are going to be sent. Figure 6.5-1 visualizes this scenario.

Figure 6.5-1: UC4 - Subscribe to be notified whenever temperature changes and is above threshold

The NGSI-LD Entity Type used is Building, also from the NGSI-LD compatible Smart Data Model[i.5] on Smart Cities. For this purpose, we are interested in the following properties of Building: - category - floorsAboveGround - floorsBelowGround - indoorTemperature - location - owner

The subscribe operation for the indoor temperature of the Building with the id "building-a85e3da145c1" and the filter on indoorTemperature greater that 30 looks as follows:

{
    "id": "urn:ngsi-ld:Subscription:storeSubscription4",
    "type": "Subscription",
    "entities": [
        {
            "id": "urn:ngsi-ld:Building:building-a85e3da145c1",
            "type": "Building"
        }
    ],
    "watchedAttributes": ["indoorTemperature"],
    "q": "indoorTemperature>30",
    "notification": {
        "format": "normalized",
        "endpoint": {
            "uri": "http://localhost:8080",
            "accept": "application/json"
        }
    }
}

Excerpt of resulting notification:

{
    "id": "urn:ngsi-ld:Notification:515236543545",
    "type": "Notification",
    "subscriptionId": "urn:ngsi-ld:Subscription:storeSubscription4",    
    "data": {
      "id": "urn:ngsi-ld:Building:building-a85e3da145c1",
      "type": "Building",
      "address": {
        "type": "Property",
        "value": {
          "addressLocality": "London",
          "postalCode": "EC4N 8AF",
          "streetAddress": "25 Walbrook"
        }
      },
      "category": {
        "type": "Property",
        "value": [
          "office"
        ]
      },
      “indoorTemperature": {
        "type": "Property",
        "value": 31.3,
      }
      ...
    }
}

The advantages for the application are the following: - Application can subscribe to be notified whenever the specified information changes(“indoor temperature of a building”) - Application gets notification on change - Application can request to only be notified in case a value is above a certain threshold (indoorTemperature>30)

In order to do this, the application needs to know the following: - Data model: - type: Building - Property: indoorTemperature (and its value, e.g. that Celsius scale is used) - Root URL: localhost:9090