Events

Events are notifications triggered by a Thing to inform about specific occurrences or changes. These are used for asynchronous communication, allowing Things to push updates to clients without requiring constant polling. For example, a motion sensor might emit an event when movement is detected. Events are typically consumed through subscription mechanisms, such as WebSockets or MQTT.

  • Events are immutable once triggered; they only represent a past occurrence.
  • Each event contains a timestamp to indicate when it was emitted.

Add Events to a Thing

  1. In the Overview panel of a Thing, click the plus icon next to Events.
    The New Event dialog opens.
  2. Enter the Event Key value. This should be a descriptor of the Event.
  3. If desired, enter a Title, any optional descriptors and the data type for this Event.
    Figure 1.


  4. Click Create.
    The information is added to the schema.
    "events": {
  "overheating": {
    "data": {
      "type": "string"
      },
   "description": "Lamp reaches a critical temperature",
    "title": ""
  }
},
  5. Once the Event has been created, you can click on the Edit icon to make further changes to this Event.
    Figure 2.


Events Detailed Information

Events are defined similarly to Properties and Actions. They allow for several metadata keys to describe what the event is, and those metadata keys follow a standard format.

The following keys can be used to describe an event:

Table 1. All Events can use the following metadata keys
Metadata Definition Description Required? Type
title Title of the Event No string
description Additional content to tell the user what the event is for. No string
data Defines the expected format of the event body. No object
The difference in defining Events is the data key. The data key is what stores the information that describes what each event should look like. The information expected in an event (as defined in the data key of the Thing description) can be any one of the following primitive types:
array
Expects a list of results
boolean
Expects a true/false
number
Expects any real number
integer
Expects any whole number
object
Expects a JSON object with additional properties defined.
string
Expects a series of letters and/or numbers
null
Expects no value

Each of these primitive types can be further defined by any or all of the following metadata keys.

Table 2. All data types can use the following metadata keys
Metadata Definition Description Required? Type
title Title of the event data displayed in the UI. No string
description Additional content to tell the user what the event data is for. No string
type Primitive data type for validation of the event data. No string
unit Provides a reference unit, especially for numbers and integers. No string
readOnly Validates that a value should not be written to. Yes (default is false) boolean
Note: In the Web of Things specification from W3C, many more metadata keys are allowed. Those are not yet supported. These include "enum", "titles", "descriptions", "@type", "const", "oneOf", "writeOnly", and "format". Nor do we support "items", "minItems" or "maxItems" on Arrays, as well as "properties" or "required" on Objects yet.
Table 3. Number data types can also use the following metadata keys (plus those in "All")
Metadata Definition Description Required? Type
minimum Minimum value. Used for validation. No number
maximum Maximum value. Used for validation. No number
Table 4. Integer data types can also use the following metadata keys (plus those in "All")
Metadata Definition Description Required? Type
minimum Minimum value. Used for validation. No integer
maximum Maximum value. Used for validation. No integer
Note: "String", "boolean" and "null" event data types do not offer any additional definition beyond what is allowed in "all"