Actions

An Action is a named element that describes a unit of executable functionality.

An Action has a name modifier: 

<Action Name="RotateCameraAction" Documentation="Simple Action to Rotate IP-based Camera by x degrees"/>

An Action must define executable code in any Atomic Domain Languages (Workflow, FacetScript, TQL, Subscribe, Sequence) or any of their combinations, within one of the following elements:

•  ThingFacet
• AppFacet
• Subscribe
• Sequence

NOTE: In the case of ThingFacet or AppFacet an Action must start with a Workflow.

Action is associated with attribute(s)

An Action must be associated or attached to a Model or Model Facet Attribute. In ThingFacets or AppFacets, an Action is associated with an attribute of the same ThingFacet or AppFacet using the "KnownBy" modifier as below.

<Double Name="RotateValue" KnownBy="RotateCameraAction"/>

Please refer to <subscribe> and <sequence> for their respective action associations.

Action results in the change of attributes' "Known" value(s)

From the Action, using the output of the workflow, you can update any attributes of the ThingFacet or AppFacet. Note that It is always the "Known" value of the attribute that will be updated by Actions. In this example, Action is changing the State and Image Attributes.

<Output name="Result" as="ActionResult">
  <Value>
    <State>[%:[%:@Output:%]/if([:IOK:]) then 'ON' else 'OFF':%]</State>
    <Image>[%:[%:@Output:%]/if([:IOK:]) then Invoke/GetImage/Message/Value/text() else '/img/no-image.jpg':%]</Image>
  </Value>
</Output>

Action Trigger

Trigger is an execution phase of an Action. Execution of an Action is asynchronous and can be triggered in any number of ways. Please refer to <subscribe> and <sequence> for their respective action triggers.

In case of ThingFacet / AppFacet Action can be triggered as a result of :

• External devices (sensors / actuators) changing their state
• Internal Models changing the state of Attributes using TQL Queries
• External applications using TQL Queries. For example, to Instantiate a Device, we use a TQL Query:
  

<Query>
  <Save format="version,current">
    <RfidReader ReaderId="R1" URL="perif://">
        <RFID value="$Null()" version="1"/>
    </RfidReader>
  </Save>
</Query>

Automatic Action Trigger

In case of certain devices - like sensors which send data continuously, one can set the trigger of action  execution to happen automatically using update="auto" attribute at the time of Action association. For example:

<Integer Name="SensorValue" update="auto" KnownBy="PhidgetSensorAction"/>

Normally, all thing updates are initiated by their correspondent [cached] model instance update. I.e. you set Image attribute of camera model to null (or other value) in order to initiate image update workflow which is normally a request/response exchange with the camera. Some devices, however, do not follow this communication pattern. Instead, they need to be put in a waiting state and then will “spontaneously” generate an event.

<Action name="RFIDReaderAction" documentation="Read RFID tag and update the instance">
  <Workflow Limit="1" Live="1" Timeout="-1">
    <Task name="Main" while="true">
      <Event name="Argument" as="ActionArgument"/>
      <Invoke name="ReadId" waitFor="Argument" get="[%:Event.Argument.URL.Value:%]"/>
      <Output name="Result" as="ActionResult">
        <Value>
          <RFID>[%:[%:@Output:%]Invoke.ReadId.Message.Value:%]</RFID>
        </Value>
      </Output>
    </Task>
  </Workflow>
</Action>

For example, if you initiate an RFID reader in standard fashion, it will wait for ONE reader event, update the known value of its model instance and stop. You’ll need to update its instance again to make it wait for the next event and so on. Update=”auto” allows to automate such workflow re-activation. Every time it processes an event, thing workflow will automatically restart itself to be ready for the next device event. This way you can have a continuous stream of events from the device without explicit request/re-activation after each one.

Note that using this option without any device throttling may result in continuous infinite loop of device updates, so it is most suitable for the devices which normally only generate events in response to external actions (e.g. detecting a RFID tag in reader’s proximity). That is, RFID workflow DOES NOT solicit device events by itself, it only listens for them. In case of IP camera snapshot, the situation would be very different because camera workflow actually asks the camera to produce one, so if you automatically restart it then it will ask again and again and again. While this may be a desirable behavior, caution must be exercised to limit the rate of such requests (for example, you can put a 1 sec delay on the get snapshot invoke to ensure that it will always wait at least a second before asking for the next snapshot).

Note that streaming of events / message from devices normally happens via Protocol Handler that is invoked. Protocol Handlers may provide additional parameter to facilitate throttling.