ThingFacet is a reusable TQL component that defines the software interactions with a "thing" and represent the "thing" in the software. A "thing" can be sensors, actuators, devices, or a particular aspect or function of a more complex machine. A ThingFacet has Attributes and Actions.
Attributes are containers of values. They can be used for the following purposes:
(1) Store parameters required to make a protocol specific invocation to the thing, such as <String Name="InterfacePort"/>
(2) Store information received from the thing, such as <Number Name="TempValue"/> (The TempValue from the temperature sensor)
(3) Hold fixed information about the thing, such as <String Name="Unit" default="Celsius"/>
(4) Act as control variables - variable that can activate certain actions. They are called "actionable attributes". Actionable attributes are linked with one or more actions in the same ThingFacet by a modifier "KnownBy". For example: <Number Name="TempValue" KnownBy="SerialReadAction"/>
Action is where the processes to interact with things are defined.