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 I. Hardware Setup

In order to run the tutorial, you need to set up the hardware. If you are using Raspberry Pi and Arduino, the instructions are here. If you are using Libelium, the instructions are here.

II. Abstract the device using ThingFacet

Write a ThingFacet 

To abstract the interactions with the temperature/humidity sensors setup in the previous section, we create a TempFacetSerial ThingFacet. 

We add two types of attributes in this ThingFacet (1) parameters required to make a protocol specific invocation (2) attribute(s) to store the information received from the sensor. For the purpose of this tutorial we have protocol specific parameters as (Unit, Peripheral, InterfacePort, Interface, etc). Temperature Value will be stored in numeric TempValue Parameter. 

<ThingFacet Name="TempFacetSerial">
	<String Name="TempValue"/>
    <String Name="Unit" default="Celsius"/>
	<String Name="Peripheral"/>
    <String Name="InterfacePort"/>
    <String Name="Interface"/>
    <String Name="UniqueId" default="56789"/>
    <String Name="Baudrate"/>
    <String Name="Format" default="ascii"/>
    <String Name="Operation"/>
    <String Name="Payload"/>
	...
</ThingFacet>

Write an Action with Workflow

The next step in ThingFacet is writing a Action which contains a workflow responsible for making external protocol specific call and store the output in the appropriate ThingFacet attribute.  An important decision while writing Action is correct protocol selection. See the /wiki/spaces/TQLDocs/pages/1179871 in the Working with Things section. For this serial sensor we need the perif:// protocol handler, which is part of the TQLEngine.

1. Write an Action name as SerialReadAction

<ThingFacet Name="TempFacetSerial">
	...
	<Action Name="SerialReadAction">
		...
	</Action>
</ThingFacet>

2. Create a Workflow within the Action, with one single continuous running Task and waiting for the Event with its ActionArgument.

<Action Name="SerialReadAction">
	<Workflow Limit="1" Live="1" Timeout="-1">
    	<Task name="Main" while="true">
        	<Event name="Argument" as="ActionArgument"/>
			...
    	</Task>
	</Workflow>
</Action>

Here we used three modifiers for this workflow. Limit = "1" means there can be at most one instance of this workflow waiting. Live = "1" means there can be at most one instance of this workflow running. Timeout ="-1" means this workflow will never be timed out. We used a modifier while = "true" with the Task to make the workflow running in a continuous loop, because it needs to run repeatedly, not just once. For more details, refer to workflow modifiers and the lifecycle of a workflow.

The task will be activated by the event handler Event called ActionArgument. "ActionArgument" is the event generated whenever the attribute(s) associated with this Action is modified (See Associate Action with a ThingFacet Attribute). ActionArgument carries all the current values of the ThingFacet attributes, which can be used in the task if needed.

3. Invoke PERIF call: Method of PERIF is GET. We use Invoke modifier Get for this purpose. The parameters required PERIF are passed as part of <Message> and <Value>. More details of the perif:// handler are in the Working with Things Section.

<Invoke name="InvokeSerialRead" waitFor="Argument" get="perif://">
    <Message>
        <Value>
            <InterfacePort>"[%:Event.Argument.interfacePort.Value:%]"
            </InterfacePort>
            <Baudrate>"[%:Event.Argument.Baudrate.Value:%]"</Baudrate>
            <Interface>"[%:Event.Argument.Interface.Value:%]"</Interface>
            <UniqueId>"[%:Event.Argument.UniqueId.Value:%]"</UniqueId>
            <Operation>"[%:Event.Argument.Operation.Value:%]"</Operation>
            <format>"[%:Event.Argument.Format.Value:%]"</format>
            <Payload>"[%:Event.Argument.Payload.Value:%]"</Payload>
            <Peripheral>"[%:Event.Argument.Peripheral.Value:%]"</Peripheral>
        </Value>
    </Message>
</Invoke>

Here Invoke gets the attribute values that the Event ActionArgument (or Argument) carries. It uses them as the parameter values for the PERIF by substitution. For example, 

<Baudrate>"[%:Event.Argument.baudrate.Value:%]"</Baudrate>

means replacing the value of Message.Value.Baudrate with the value of Event.Argument.baudrate.Value.

Value substitution (rather than assignment) is very common in TQL, given that it is a declarative language. The notation [%: is part of the /wiki/spaces/TEACH/pages/21170773. More details on /wiki/spaces/TEACH/pages/21170773 can be found in the Developer's Guide.

4. Process the message received from the sensor

<Output Name="Result" As="ActionResult">
	<Value>
    	<TempValue>
        	[%:Invoke.InvokeSerialRead.Message.Value/number(substring-before(substring-after("[%:Invoke.InvokeSerialRead.Message.Value.received:%]",'#TCB:'), '#')):%]
    	</TempValue>
	</Value>
</Output>

Here we used an XPath statement to pass the message. Alternatively, you can use Javascript. An example of using JavaScript for message processing within an Action can be found in another tutorial here.

Associate Action with a ThingFacet Attribute

We will now have to associate a ThingFacet Attribute (TempValue) with the Action using the KnownBy modifier. When TempValue is "KnownBy" SerialReadAction, any TempValue value changes will activate the SerialReadAction.

<ThingFacet Name="TempFacetSerial">
	...
	<String Name="TempValue" update="auto" KnownBy="SerialReadAction"/>
</ThingFacet>

The attribute modifier update= "auto" makes sure that once the action associated with this attribute is triggered, its workflow continues to run and wait for subsequent sensor events (not just the first event). This modifier is only used with actionable attributes. For more details, refer to Automatic Action trigger.

III. Combine ThingFacet with a ThingModel to persist data

Finally, in order to use ThingFacet we have to combine it with a ThingModel. We define ThingModel to contain only a unique system identifier.

<ThingModel Name="TempSensor" combines="TempFacetSerial">
	<Sid Name="sensorId"/>
</ThingModel>

Only when the TempSensor ThingModel "combines" TempFacetSerial, can TempFacetSerial be instantiated within the TempSensor and accessible by TQL queries. TempSensor will inherit all the attributes from TempFacetSerial, in addition to its own attributes. The ThingFacet TempFacetSerial hence serves as a reusable component.

More details on the use of "combines" can be found here. Information on Sid can be found here.

IV. Deploy and test via queries and subscriptions

Export, import and deploy

Once the models are built in a TQLStudio project, you can export the project. The URL of the Zip file containing the content of your project will be sent over to your email account. Once you have downloaded the engine – launch the TQLEngine User Interface in the browser and select Import Project. You can copy the URL from Export Project Email and hit import button. Go to ThingSpaces and Deploy the project.

Instantiation

Here we use a query to instantiate the sensor, creating 1 instance of the TempSensor ThingModel. In the query, we first use "DeleteAll" to delete all the current instances of the TempSensor, if there are any. The Save will save the values into the corresponding model attributes  (inherited from the ThingFacet). These values provide the runtime parameters for the perif:// handler, as well as providing an update of the TempValue actionable attribute ($Null ( )), which will trigger the associated action SerialReadAction.

<Query>
	<DeleteAll format="version,current">
    	<TempSensor>
      		<sensorId ne=""/>
    	</TempSensor>
  	</DeleteAll>
  	<Save format="version,current">
    	<!-- This will read -->
    	<TempSensor>
      		<Peripheral>serial</Peripheral>
      		<Baudrate>115200</Baudrate>
      		<InterfacePort>/dev/cu.usbserial-DA01OX0S</InterfacePort>
      		<Interface>serial</Interface>
      		<Format>ascii</Format>
      		<Operation>receive</Operation>
      		<UniqueId>76522</UniqueId>
      		<Payload>$Null()</Payload>
      		<TempValue>$Null()</TempValue>
    	</TempSensor>
  	</Save>
</Query>

Query and subscription

Now we can try a simple Find Query to get sensor values

<Query>
    <Find format="version,known">
        <TempSensor>
            <sensorId ne="" />
        </TempSensor>
    </Find>
</Query>

You will see the result from the RESULTS window:

<Find Status="Success" Format="version,current">
    <Result>
        <TempSensor>
            <sensorId>KLHEPDF7AAAAUAABB4JDTW4S</sensorId>
            <interfacePort Value="/dev/cu.usbserial-A7030IWB" Version="1"/>
            <payload Value="" Version="1"/>
            <peripheral Value="serial" Version="1"/>
            <interface Value="serial" Version="1"/>
            <operation Value="receive" Version="1"/>
            <tempValue Value="" Version="1"/>
            <baudrate Value="115200" Version="1"/>
            <uniqueId Value="76522" Version="1"/>
            <format Value="ascii" Version="1"/>
        </TempSensor>
    </Result>
</Find>

<Query Storage='TqlSubscription'>
    <Save>
        <TqlSubscription Label='TempSensor' sid='20'>
            <Topic>*Atomiton.Sensor.TempSensor*</Topic>
        </TqlSubscription>
    </Save>
</Query>

<Topic>Atomiton.Sensor.TempSensor.TempValue*</Topic>

V. Source Code

Import into TQLStudio

The full content of the code is here.

<Namespace Name="Atomiton">
    <Domain Name="Sensor">
		<ThingFacet Name="TempFacetSerial">
			<String Name="TempValue" update="auto" KnownBy="SerialReadAction"/>    
    		<String Name="Unit" default="Celsius"/>
    		<String Name="Peripheral"/>
    		<String Name="InterfacePort"/>
    		<String Name="Interface"/>
    		<String Name="UniqueId" default="56789"/>
    		<String Name="Baudrate"/>
    		<String Name="Format" default="ascii"/>
    		<String Name="Operation"/>
    		<String Name="Payload"/>
			<Action Name="SerialReadAction">
        		<Workflow Limit="1" Live="1" Timeout="-1">
    				<Task name="Main" while="true">
        				<Event name="Argument" as="ActionArgument" />
        				<Invoke name="InvokeSerialRead" waitFor="Argument" get="perif://">
            				<Message>
        						<Value>
            						<InterfacePort>"[%:Event.Argument.interfacePort.Value:%]"</InterfacePort>
            						<Baudrate>"[%:Event.Argument.baudrate.Value:%]"</Baudrate>
            						<Interface>"[%:Event.Argument.interface.Value:%]"</Interface>
            						<UniqueId>"[%:Event.Argument.uniqueId.Value:%]"</UniqueId>
            						<Operation>"[%:Event.Argument.operation.Value:%]"</Operation>
            						<format>"[%:Event.Argument.format.Value:%]"</format>
            						<Payload>"[%:Event.Argument.payload.Value:%]"</Payload>
            						<Peripheral>"[%:Event.Argument.peripheral.Value:%]"</Peripheral>
        						</Value>
    						</Message>
        				</Invoke>
        				<Output name="Result" as="ActionResult">
            				<Value>
                				<tempValue>[%:Invoke.InvokeSerialRead.Message.Value/number(substring-before(substring-after
                					("[%:Invoke.InvokeSerialRead.Message.Value.received:%]",'#TCB:'), '#')):%]
        						</tempValue>
            				</Value>
        				</Output>
    				</Task>
				</Workflow>
    		</Action>
		</ThingFacet>
		<ThingModel Name="TempSensor" combines="TempFacetSerial">
    		<Sid Name="sensorId"/>
		</ThingModel>
	</Domain>
</Namespace>