System ID (Sid)

SystemId or Sid is a unique identifier automatically assigned by A-Stack to every newly created Model Instance. It is of type "String" and is defined as the following in TQL.

#
Def(name: "System", inherits: "Entity", documentation: "Marker of all system types")
Def(name: "SystemId", alt: "sid", inherits: "String,System")

Note: SystemId and Sid are synonyms. For the purpose of this document will use Sid when referring to System ID.

Model developers can define attribute of type SystemId or Sid.

In this example: PhidServoId is defined as Sid.

#
ThingModel(Name: "PhidgetServoModel", Combines: "PhidgetServoFacet")
  Sid(Name: "PhidServoId")

When the Model Instance is created, using Create TQL Query, System ID value is automatically generated by A-Stack.

#
Query:
  Create:
    PhidgetServoModel:
      ServoProtocolURL: "phid://"
      ServoProtocolURL:
		PhidgetDeviceType: "PhidgetAdvancedServo"
      DeviceInterfaceIndex: 0
      ServoAngle: 110

Using the Find TQL Query on PhidgetServoModel

#
Query:
  Find:
    PhidgetServoModel:
      PhidServoId(ne: "")

Find Result is:

#
Find(Status="Success"):
  Result:
    PhidgetServoModel:
      PhidServoId: "KNI5JYVPAAAAUAABA4ONNHF2"
      PhidgetDeviceType: "PhidgetAdvancedServo"
      ServoAngle: 110
      DeviceInterfaceIndex: 0
      ServoProtocolURL: "phid://"

Note that the PhidServoId value is automatically generated even though it is NOT specified at the time of Create Query

#
PhidServoId: "KNI5JYVPAAAAUAABA4ONNHF2"

About System ID:

• Have unique values per Installation of A-Stack: System ID Values are guaranteed to be Unique for a given Installation of A-Stack.
• Value can neither be given or modified by user: If an attribute is defined of type Sid or SystemId, their values can neither be specified or updated by the user.
• New values are generated each time for same model: Each time an instance is deleted and created again new value System ID value.