Learn only as yourself 《 The development of the Internet of things 》 Learning notes of , Link to the original course ： Geek time 《 The development of the Internet of things 》—— Guo Chaobin

In the Internet of things , How to provide the control interface information of the underlying hardware ？ How does the platform application match with devices of different brands （ Development ）？

We need to solve this problem , By adding an intermediate protocol layer , For example, browse different files in the browser （ Text 、 Audio and video etc. ） Through HTML（ Hypertext markup language ） To express , The Internet of things has a similar protocol layer ——Thing Specification Language, abbreviation TSL.

Use TSL Describe the entity model in the Internet of things , Namely ” Models of things , Or called “ product model ”, It's also called “ Data panel ” Of .

What is the relationship between IOT model and equipment ？

The object model is an abstraction of the physical world , After digital description , A digital model for the digital world . Direct point , Object model is a language that can be understood by computer , Make it clear what this product is 、 What can be done , And what information can be provided .

In turn, , The object model also specifies the function of the equipment . New equipment , If it's the same type , In the design 、 Under development , Will follow the same functional definition , Have the same characteristics , Implement the same service .

How to define the object model

We usually use attributes 、 Event and action are three functional elements to define .

attribute （Property）： Describe a certain state when the product is running , Property can be read and written , For example, the two properties of temperature and humidity of environmental detection equipment .

event （Event）： Summarize the information generated during the operation of the equipment 、 Warnings and faults, etc , It's an event. . The event is reported by the equipment , Cannot be set by app .

action （Action）： Also known as services , The action is sent to the device by the application , The device can return results to the application . Actions can be further divided into synchronous and asynchronous .

Data type of object model

There are six types of object models ：

1. Boolean type （Bool）： Non true or false binary variables .
2. Integer type （Int）： Linearly adjustable integer variables .
3. String type （String）： A variable expressed as a string .
4. floating-point （Float）： Variables with floating-point precision .
5. enum （Enum）： Custom finite set values .
6. Time type （Timestamp）：String Type of UTC Time stamp .

Physical type is generally used JSON Format to express model elements .JSON yes Web In development , Frequently used data formats .

Define the IOT model of intelligent electric lamp

Intelligent electric switch attribute Corresponding JSON Say as follows ：

{
    
	"id": "power_switch",  //  The identification of the property 
	"name": " Light switch ",      //  name 
	"desc": " Light switch control ",   //  Description of the property 
	"required": true,       //  Indicates whether this property must contain 
	"mode": "rw",           //  Attribute mode , Set to read and write 
	"define": {
                 //  The numeric definition of the property 
		"type": "bool",     //  Type of value , Boolean type 
		"mapping": {
            //  The meaning of specific values 
			"0": " Turn off ",        
			"1": " open "
		}
	}
}

Intelligent electric lamp event , The voltage of the light needs to be monitored , When the voltage is too low , You can report this event （ The voltage is too low ）, The data type is floating point , Corresponding JSON The format is described below ：

{
    
	"id": "voltage_too_low",  //  Identification of the event 
	"name": " The light is too low ",         //  name 
	"desc": " The voltage is too low ",         //  Description of the event 
	"required": false,        //  Indicates whether this property must contain 
	"params": [               //  Parameters of the event 
		{
                 
			"id": "voltage",       //  Identification of event parameters 
			"name": " voltage ",         //  name 
			"desc": " The current voltage ",      //  Description of parameters 
			"define": {
                 //  Numerical definition of parameters 
				"type": "float",    //  Type of value , floating-point 
				"unit": "V",        //  The unit of value , Volt 
				"step": "1",        //  The change step of the value  
				"min": "0.0",       //  The minimum value of the value 
				"max": "24.0",      //  The maximum value of the value 
				"start": "1",       //  The starting value of the event 
			}
		}
	]
}

action Definition and properties of 、 The process of defining events is similar to .

Should each model be defined from scratch ？

When creating a model , Yes Copy and Inherit Two modes , Their differences are reflected in the model relationship .

Copy mode is similar to value copy in programming , The new model has exactly the same elements as the copied model , The two models are independent of each other , Model changes do not affect each other .

Inheritance pattern is the concept of inheritance in programming , The new model is defined as “ Submodels ”, The inherited model is defined as “ Parent model ”.

Extended application of object model

Device shadow

Device shadow is used for Cache device status . The application can directly obtain the last updated attribute value of the device through the device shadow , Without having to access the device every time . When the device is online , Application instructions can be obtained directly ; When the device is offline , When you go online again, you can actively pull application instructions .

such as , The switching state of the smart light is a property , You can change... Locally through physical switches , If the network is unstable , Then the state on the platform may not be synchronized with the real state . Device shadow can be synchronized in both directions , Realize the consistency between the server and the device , To solve this problem .

Number twin （Digital Twin）

Object model is the digital model of physical entity , But it is mainly aimed at the development of applications and equipment interoperability in the Internet of things . This model integrates all kinds of data of physical entities , These data will evolve with the physical entity in the life cycle of the physical entity , Accumulate all kinds of information and knowledge , And promote the optimization of physical entities . Such a model is the digital twin of physical entities .