TQLEngine stores the following variables/data of each model instance:
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Attribute values
Attribute know
Version number of each attribute value?
Timestamp of ____
..There are three types of Models that can be defined at the time of creating models for your IoT applications. The three models are:
- DataModel
- ThingModel
- AppModel
See Models for details.
In TQL Model development is a three step process -
- Definition
- Deploy (compilation)
- Queries (instantiation, update, delete, subscription)
See also lifecycle of models.
Model Instances
Once models are defined and deployed the meta structure of the model definition is stored in memory. (If A-Stack shuts down and restart, the model definitions will be reloaded. The but model instance data will persist.)
Before Find queries can find anything from the models, they must be instantiated, or populated with data. The result of model instantiation is called Model Instances. Multiple model instances can be created from the same model (definition). Model instance data is persisted in the storage (TQLCache), as defined at the time of the deployment.
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Even though A-Stack uses SQL type of database technology to persist model instances, they are stored in a schema-less way, not in a relational format. This preserves the the performance at scale. |
For example: Here is the definition of a ThingModel - PhidgetSensorModel that combines PhidgetSensorFacet.
Definition
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ThingFacet(Name: "PhidgetSensorFacet"):
Integer(Name: "SensorValue", Update: "auto", KnownBy: "PhidgetSensorAction")
String(Name: "SensorURL", Default: "phid://")
String(Name: "SensorInterfaceIndex")
String(Name: "SensorType")
String(Name: "SensorInterfaceType")
String(Name: "SensorValueFormat")
String(Name: "Simulated")
ThingModel(Name: "PhidgetSensorModel", Combines: "PhidgetSensorFacet"):
Sid(Name: "phidId") |
Create model instances
The model instances of PhidgetSensorModel is created using a Create TQL Query.
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Query:
Create:
PhidgetSensors:
SensorURL: phid://
SensorType: Rotation
SensorInterfaceType: PhidgetInterfaceKit
SensorValueFormat: Raw
SensorInterfaceIndex: 0
SensorValue(value: "$Null()", version: "1");
Simulated: true |
The result of model instance creation is below.
Note that there is Status returned for every attribute that gets created.
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Create(Status: "Success"):
PhidgetSensors:
phidId: KNUBPHLOAAAAUAABA6EJCI75
SensorValue(Status: "Success+Created:1:1457740291438;", Value: "", Version: "1")
SensorURL(Status: "Success+Created:1:1457740291442;", Value: "phid://", Version: "1")
SensorInterfaceIndex(Status: "Success+Created:1:1457740291443;", Value: "0", Version: "1")
SensorType(Status: "Success+Created:1:1457740291444;", Value: "Rotation", Version: "1")
SensorInterfaceType(Status: "Success+Created:1:1457740291444;", Value: "PhidgetInterfaceKit", Version: "1")
SensorValueFormat(Status: "Success+Created:1:1457740291445;", Value: "Raw", Version: "1")
Simulated(Status: "Success+Created:1:1457740291445;", Value: "true", Version: "1") |
Find Model Instances
After model instances are created, you can read them using Find Query with constraints.
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Query:
Find format: "all"):
PhidgetSensors:
SensorURL(ne : "") |
Find Query Result
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#Find(Status: "Success", Format: "all"):
Result:
PhidgetSensors(QName: "SimpleModel.MyModels.PhidgetSensors"):
phidId: KNUBPHLOAAAAUAABA6EJCI75
SensorValue(Value: "", Known: "60", Version: "1", Timestamp: "1457740291438", DateTime: "2016-03-11 15:51:31.438", QName: "SimpleModel.MyModels.PhidgetSensors.SensorValue", FName: "SensorValue")
SensorURL(Value: "phid://", Known: "phid://", Version: "1", Timestamp: "1457740291442", DateTime: "2016-03-11 15:51:31.442", QName: "SimpleModel.MyModels.PhidgetSensors.SensorURL", FName: "SensorURL")
SensorInterfaceType(Value: "PhidgetInterfaceKit", Known: "PhidgetInterfaceKit", Version: "1", Timestamp: "1457740291444", DateTime: "2016-03-11 15:51:31.444", QName: "SimpleModel.MyModels.PhidgetSensors.SensorInterfaceType", FName: "SensorInterfaceType")
Simulated(Value: "true", Known: "true", Version: "1", Timestamp: "1457740291445", DateTime: "2016-03-11 15:51:31.445", QName: "SimpleModel.MyModels.PhidgetSensors.Simulated", FName: "Simulated")
SensorInterfaceIndex(Value: "0", Known: "0", Version: "1", Timestamp: "1457740291443", DateTime: "2016-03-11 15:51:31.443", QName: "SimpleModel.MyModels.PhidgetSensors.SensorInterfaceIndex", FName: "SensorInterfaceIndex")
SensorType(Value: "Rotation", Known: "Rotation", Version: "1", Timestamp: "1457740291444", DateTime: "2016-03-11 15:51:31.444", QName: "SimpleModel.MyModels.PhidgetSensors.SensorType", FName: "SensorType")
SensorValueFormat(Value: "Raw", Known: "Raw", Version: "1", Timestamp: "1457740291445", DateTime: "2016-03-11 15:51:31.445", QName: "SimpleModel.MyModels.PhidgetSensors.SensorValueFormat", FName: "SensorValueFormat") |
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The following system generated tags are for each attribute:
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Status: This is a transient attribute returned as part of the result of TQL Create/Save, Update and Delete operations. It is not persisted.