Manage digital twins

Entities in your environment are represented by digital twins. Managing your digital twins may include creation, modification, and removal.

This article focuses on managing digital twins; to work with relationships and the twin graph as a whole, see Manage the twin graph and relationships.

Tip

All SDK functions come in synchronous and asynchronous versions.

Prerequisites

To work with Azure Digital Twins in this article, you first need to set up an Azure Digital Twins instance. You also need the required permissions for using it. If you already have an Azure Digital Twins instance set up, you can use it instead.

Otherwise, follow the instructions in Set up an instance and authentication. The instructions contain information to help you verify that you've completed each step successfully.

After you set up your instance, make a note of the following values. You'll need these values to connect to the instance later:

  • The instance's host name. You can find the host name in the Azure portal.
  • The Azure subscription that you used to create the instance. Either its name or its ID will work. You can find the subscription on your instance's Overview page in the Azure portal.

Developer interfaces

This article highlights how to complete different management operations using the .NET (C#) SDK. You can also craft these same management calls using the other language SDKs described in Azure Digital Twins APIs and SDKs.

Other developer interfaces that can be used to complete these operations include:

Visualization

Azure Digital Twins Explorer is a visual tool for exploring the data in your Azure Digital Twins graph. You can use the explorer to view, query, and edit your models, twins, and relationships.

To read about the Azure Digital Twins Explorer tool, see Azure Digital Twins Explorer. For detailed steps on how to use its features, see Use Azure Digital Twins Explorer.

Here's what the visualization looks like:

Screenshot of Azure Digital Twins Explorer showing sample models and twins.

Create a digital twin

To create a twin, you use the CreateOrReplaceDigitalTwinAsync() method on the service client like this:

await client.CreateOrReplaceDigitalTwinAsync<BasicDigitalTwin>(twinId, initData);

To create a digital twin, you need to provide:

  • The desired ID for the digital twin, which you are defining at this stage
  • The model you want to use

Optionally, you can provide initial values for all properties of the digital twin. Properties are treated as optional and can be set later, but they won't show up as part of a twin until they've been set.

Note

While twin properties don't have to be initialized, any components on the twin do need to be set when the twin is created. They can be empty objects, but the components themselves must exist.

The model and any initial property values are provided through the initData parameter, which is a JSON string containing the relevant data. For more information on structuring this object, continue to the next section.

Tip

After creating or updating a twin, there may be a latency of up to 10 seconds before the changes will be reflected in queries. The GetDigitalTwin API (described later in this article) does not experience this delay, so if you need an instant response, use the API call instead of querying to see your newly-created twins.

Initialize model and properties

You can initialize the properties of a twin at the time that the twin is created.

The twin creation API accepts an object that is serialized into a valid JSON description of the twin properties. See Digital twins and the twin graph for a description of the JSON format for a twin.

First, you can create a data object to represent the twin and its property data. You can create a parameter object either manually, or by using a provided helper class. Here is an example of each.

Create twins using manually created data

Without the use of any custom helper classes, you can represent a twin's properties in a Dictionary<string, object>, where the string is the name of the property and the object is an object representing the property and its value.

// Define a custom model type for the twin to be created

internal class CustomDigitalTwin
{
    [JsonPropertyName(DigitalTwinsJsonPropertyNames.DigitalTwinId)]
    public string Id { get; set; }

    [JsonPropertyName(DigitalTwinsJsonPropertyNames.DigitalTwinETag)]
    public string ETag { get; set; }

    [JsonPropertyName(DigitalTwinsJsonPropertyNames.DigitalTwinMetadata)]
    public MyCustomDigitalTwinMetadata Metadata { get; set; } = new MyCustomDigitalTwinMetadata();

    [JsonPropertyName("temperature")]
    public double Temperature { get; set; }

    [JsonPropertyName("humidity")]
    public double Humidity{ get; set; }
}

internal class MyCustomDigitalTwinMetadata
{
    [JsonPropertyName(DigitalTwinsJsonPropertyNames.MetadataModel)]
    public string ModelId { get; set; }

    [JsonPropertyName("temperature")]
    public DigitalTwinPropertyMetadata Temperature { get; set; }

    [JsonPropertyName("humidity")]
    public DigitalTwinPropertyMetadata Humidity { get; set; }
}

public class TwinOperationsSamples
{
    public async Task CreateTwinAsync(DigitalTwinsClient client)
    {
        // Initialize the twin properties
        var myTwin = new CustomDigitalTwin
        {
            Metadata = { ModelId = "dtmi:example:Room;1" },
            Temperature = 25.0,
            Humidity = 50.0,
        };

        // Create the twin
        const string twinId = "<twin-ID>";
        Response<CustomDigitalTwin> response = await client.CreateOrReplaceDigitalTwinAsync(twinId, myTwin);
        Console.WriteLine($"Temperature last updated on {response.Value.Metadata.Temperature.LastUpdatedOn}");

Create twins with the helper class

The helper class of BasicDigitalTwin allows you to store property fields in a "twin" object directly. You may still want to build the list of properties using a Dictionary<string, object>, which can then be added to the twin object as its CustomProperties directly.

string twinId = "myTwinID";
var initData = new BasicDigitalTwin
{
    Id = twinId,
    Metadata = { ModelId = "dtmi:example:Room;1" },
    // Initialize properties
    Contents =
    {
        { "Temperature", 25.0 },
        { "Humidity", 50.0 },
    },
};

await client.CreateOrReplaceDigitalTwinAsync<BasicDigitalTwin>(twinId, initData);

Note

BasicDigitalTwin objects come with an Id field. You can leave this field empty, but if you do add an ID value, it needs to match the ID parameter passed to the CreateOrReplaceDigitalTwinAsync() call. For example:

twin.Id = "myRoomId";

Get data for a digital twin

You can access the details of any digital twin by calling the GetDigitalTwin() method like this:

Response<BasicDigitalTwin> twinResponse = await client.GetDigitalTwinAsync<BasicDigitalTwin>(twinId);
twin = twinResponse.Value;

This call returns twin data as a strongly-typed object type such as BasicDigitalTwin. BasicDigitalTwin is a serialization helper class included with the SDK, which will return the core twin metadata and properties in pre-parsed form. You can always deserialize twin data using the JSON library of your choice, like System.Text.Json or Newtonsoft.Json. For basic access to a twin, however, the helper classes can make this more convenient.

Note

BasicDigitalTwin uses System.Text.Json attributes. In order to use BasicDigitalTwin with your DigitalTwinsClient, you must either initialize the client with the default constructor, or, if you want to customize the serializer option, use the JsonObjectSerializer.

The BasicDigitalTwin helper class also gives you access to properties defined on the twin, through a Dictionary<string, object>. To list properties of the twin, you can use:

BasicDigitalTwin twin;
Response<BasicDigitalTwin> twinResponse = await client.GetDigitalTwinAsync<BasicDigitalTwin>(twinId);
twin = twinResponse.Value;
Console.WriteLine($"Model id: {twin.Metadata.ModelId}");
foreach (string prop in twin.Contents.Keys)
{
    if (twin.Contents.TryGetValue(prop, out object value))
        Console.WriteLine($"Property '{prop}': {value}");
}

Only properties that have been set at least once are returned when you retrieve a twin with the GetDigitalTwin() method.

Tip

The displayName for a twin is part of its model metadata, so it will not show when getting data for the twin instance. To see this value, you can retrieve it from the model.

To retrieve multiple twins using a single API call, see the query API examples in Query the twin graph.

Consider the following model (written in Digital Twins Definition Language (DTDL)) that defines a Moon:

{
    "@id": "dtmi:example:Moon;1",
    "@type": "Interface",
    "@context": "dtmi:dtdl:context;2",
    "contents": [
        {
            "@type": "Property",
            "name": "radius",
            "schema": "double",
            "writable": true
        },
        {
            "@type": "Property",
            "name": "mass",
            "schema": "double",
            "writable": true
        }
    ]
}

The result of calling object result = await client.GetDigitalTwinAsync("my-moon"); on a Moon-type twin might look like this:

{
  "$dtId": "myMoon-001",
  "$etag": "W/\"e59ce8f5-03c0-4356-aea9-249ecbdc07f9\"",
  "radius": 1737.1,
  "mass": 0.0734,
  "$metadata": {
    "$model": "dtmi:example:Moon;1",
    "radius": {
      "desiredValue": 1737.1,
      "desiredVersion": 5,
      "ackVersion": 4,
      "ackCode": 200,
      "ackDescription": "OK"
    },
    "mass": {
      "desiredValue": 0.0734,
      "desiredVersion": 8,
      "ackVersion": 8,
      "ackCode": 200,
      "ackDescription": "OK"
    }
  }
}

The defined properties of the digital twin are returned as top-level properties on the digital twin. Metadata or system information that is not part of the DTDL definition is returned with a $ prefix. Metadata properties include the following values:

  • $dtId: The ID of the digital twin in this Azure Digital Twins instance
  • $etag: A standard HTTP field assigned by the web server. This is updated to a new value every time the twin is updated, which can be useful to determine whether the twin's data has been updated on the server since a previous check. You can use If-Match to perform updates and deletes that only complete if the entity's etag matches the etag provided. For more information on these operations, see the documentation for DigitalTwins Update and DigitalTwins Delete.
  • $metadata: A set of other properties, including:
    • The DTMI of the model of the digital twin.
    • Synchronization status for each writable property. This is most useful for devices, where it's possible that the service and the device have diverging statuses (for example, when a device is offline). Currently, this property only applies to physical devices connected to IoT Hub. With the data in the metadata section, it is possible to understand the full status of a property, as well as the last modified timestamps. For more information about sync status, see this IoT Hub tutorial on synchronizing device state.
    • Service-specific metadata, like from IoT Hub or Azure Digital Twins.

You can read more about the serialization helper classes like BasicDigitalTwin in Azure Digital Twins APIs and SDKs.

View all digital twins

To view all of the digital twins in your instance, use a query. You can run a query with the Query APIs or the CLI commands.

Here is the body of the basic query that will return a list of all digital twins in the instance:

SELECT * FROM DIGITALTWINS

Update a digital twin

To update properties of a digital twin, you write the information you want to replace in JSON Patch format. In this way, you can replace multiple properties at once. You then pass the JSON Patch document into an UpdateDigitalTwin() method:

await client.UpdateDigitalTwinAsync(twinId, updateTwinData);

A patch call can update as many properties on a single twin as you want (even all of them). If you need to update properties across multiple twins, you'll need a separate update call for each twin.

Tip

After creating or updating a twin, there may be a latency of up to 10 seconds before the changes will be reflected in queries. The GetDigitalTwin API (described earlier in this article) does not experience this delay, so use the API call instead of querying to see your newly-updated twins if you need an instant response.

Here is an example of JSON Patch code. This document replaces the mass and radius property values of the digital twin it is applied to.

[
    {
      "op": "replace",
      "path": "/mass",
      "value": 0.0799
    },
    {
      "op": "replace",
      "path": "/radius",
      "value": 0.800
    }
  ]

Note

This example shows the JSON Patch replace operation, which replaces the value of an existing property. For a full list of JSON Patch operations that can be used, including add and remove, see the Operations for JSON Patch.

When updating a twin from a code project using the .NET SDK, you can create JSON patches using the Azure .NET SDK's JsonPatchDocument. Here is an example.

var updateTwinData = new JsonPatchDocument();
updateTwinData.AppendAdd("/Temperature", 25.0);
updateTwinData.AppendAdd("/myComponent/Property", "Hello");
// Un-set a property
updateTwinData.AppendRemove("/Humidity");

await client.UpdateDigitalTwinAsync("myTwin", updateTwinData).ConfigureAwait(false);

Update sub-properties in digital twin components

Recall that a model may contain components, allowing it to be made up of other models.

To patch properties in a digital twin's components, you can use path syntax in JSON Patch:

[
  {
    "op": "replace",
    "path": "/mycomponentname/mass",
    "value": 0.0799
  }
]

Update sub-properties in object-type properties

Models may contain properties that are of an object type. Those objects may have their own properties, and you may want to update one of those sub-properties belonging to the object-type property. This process is similar to the process for updating sub-properties in components, but may require some extra steps.

Consider a model with an object-type property, ObjectProperty. ObjectProperty has a string property named StringSubProperty.

When a twin is created using this model, it's not necessary to instantiate the ObjectProperty at that time. If the object property is not instantiated during twin creation, there is no default path created to access ObjectProperty and its StringSubProperty for a patch operation. You will need to add the path to ObjectProperty yourself before you can update its properties.

This can be done with a JSON Patch add operation, like this:

[
  {
    "op": "add", 
    "path": "/ObjectProperty", 
    "value": {"StringSubProperty":"<string-value>"}
  }
]

Note

If ObjectProperty has more than one property, you should include all of them in the value field of this operation, even if you're only updating one:

... "value": {"StringSubProperty":"<string-value>", "Property2":"<property2-value>", ...}

After this has been done once, a path to StringSubProperty exists, and it can be updated directly from now on with a typical replace operation:

[
  {
    "op": "replace",
    "path": "/ObjectProperty/StringSubProperty",
    "value": "<string-value>"
  }
]

Although the first step isn't necessary in cases where ObjectProperty was instantiated when the twin was created, it's recommended to use it every time you update a sub-property for the first time, since you may not always know for sure whether the object property was initially instantiated or not.

Update a digital twin's model

The UpdateDigitalTwin() function can also be used to migrate a digital twin to a different model.

For example, consider the following JSON Patch document that replaces the digital twin's metadata $model field:

[
  {
    "op": "replace",
    "path": "/$metadata/$model",
    "value": "dtmi:example:foo;1"
  }
]

This operation will only succeed if the digital twin being modified by the patch conforms with the new model.

Consider the following example:

  1. Imagine a digital twin with a model of foo_old. foo_old defines a required property mass.
  2. The new model foo_new defines a property mass, and adds a new required property temperature.
  3. After the patch, the digital twin must have both a mass and temperature property.

The patch for this situation needs to update both the model and the twin's temperature property, like this:

[
  {
    "op": "replace",
    "path": "/$metadata/$model",
    "value": "dtmi:example:foo_new;1"
  },
  {
    "op": "add",
    "path": "/temperature",
    "value": 60
  }
]

Handle conflicting update calls

Azure Digital Twins ensures that all incoming requests are processed one after the other. This means that even if multiple functions try to update the same property on a twin at the same time, there's no need for you to write explicit locking code to handle the conflict.

This behavior is on a per-twin basis.

As an example, imagine a scenario in which these three calls arrive at the same time:

  • Write property A on Twin1
  • Write property B on Twin1
  • Write property A on Twin2

The two calls that modify Twin1 are executed one after another, and change messages are generated for each change. The call to modify Twin2 may be executed concurrently with no conflict, as soon as it arrives.

Delete a digital twin

You can delete twins using the DeleteDigitalTwin() method. However, you can only delete a twin when it has no more relationships. So, delete the twin's incoming and outgoing relationships first.

Here is an example of the code to delete twins and their relationships. The DeleteDigitalTwin SDK call is highlighted to clarify where it falls in the wider example context.

private static async Task CustomMethod_DeleteTwinAsync(DigitalTwinsClient client, string twinId)
{
    await CustomMethod_FindAndDeleteOutgoingRelationshipsAsync(client, twinId);
    await CustomMethod_FindAndDeleteIncomingRelationshipsAsync(client, twinId);
    try
    {
        await client.DeleteDigitalTwinAsync(twinId);
        Console.WriteLine("Twin deleted successfully");
    }
    catch (RequestFailedException ex)
    {
        Console.WriteLine($"*** Error:{ex.Message}");
    }
}

private static async Task CustomMethod_FindAndDeleteOutgoingRelationshipsAsync(DigitalTwinsClient client, string dtId)
{
    // Find the relationships for the twin

    try
    {
        // GetRelationshipsAsync will throw an error if a problem occurs
        AsyncPageable<BasicRelationship> rels = client.GetRelationshipsAsync<BasicRelationship>(dtId);

        await foreach (BasicRelationship rel in rels)
        {
            await client.DeleteRelationshipAsync(dtId, rel.Id).ConfigureAwait(false);
            Console.WriteLine($"Deleted relationship {rel.Id} from {dtId}");
        }
    }
    catch (RequestFailedException ex)
    {
        Console.WriteLine($"*** Error {ex.Status}/{ex.ErrorCode} retrieving or deleting relationships for {dtId} due to {ex.Message}");
    }
}

private static async Task CustomMethod_FindAndDeleteIncomingRelationshipsAsync(DigitalTwinsClient client, string dtId)
{
    // Find the relationships for the twin

    try
    {
        // GetRelationshipsAsync will throw an error if a problem occurs
        AsyncPageable<IncomingRelationship> incomingRels = client.GetIncomingRelationshipsAsync(dtId);

        await foreach (IncomingRelationship incomingRel in incomingRels)
        {
            await client.DeleteRelationshipAsync(incomingRel.SourceId, incomingRel.RelationshipId).ConfigureAwait(false);
            Console.WriteLine($"Deleted incoming relationship {incomingRel.RelationshipId} from {dtId}");
        }
    }
    catch (RequestFailedException ex)
    {
        Console.WriteLine($"*** Error {ex.Status}/{ex.ErrorCode} retrieving or deleting incoming relationships for {dtId} due to {ex.Message}");
    }
}

Delete all digital twins

For an example of how to delete all twins at once, download the sample app used in the Explore the basics with a sample client app. The CommandLoop.cs file does this in a CommandDeleteAllTwins() function.

Runnable digital twin code sample

You can use the runnable code sample below to create a twin, update its details, and delete the twin.

Set up sample project files

The snippet uses a sample model definition, Room.json. To download the model file so you can use it in your code, use this link to go directly to the file in GitHub. Then, right-click anywhere on the screen, select Save as in your browser's right-click menu, and use the Save As window to save the file as Room.json.

Next, create a new console app project in Visual Studio or your editor of choice.

Then, copy the following code of the runnable sample into your project:

using System;
using System.Threading.Tasks;
using System.Collections.Generic;
using Azure;
using Azure.DigitalTwins.Core;
using Azure.Identity;
using System.IO;

namespace DigitalTwins_Samples
{
    class TwinOperationsSample
    {
        public static async Task Main(string[] args)
        {
            Console.WriteLine("Hello World!");

            // Create the Azure Digital Twins client for API calls
            string adtInstanceUrl = "https://<your-instance-hostname>";
            var credentials = new DefaultAzureCredential();
            var client = new DigitalTwinsClient(new Uri(adtInstanceUrl), credentials);
            Console.WriteLine($"Service client created – ready to go");

            // Upload models
            Console.WriteLine($"Upload a model");
            string dtdl = File.ReadAllText("<path-to>/Room.json");
            var models = new List<string> { dtdl };
            // Upload the model to the service
            await client.CreateModelsAsync(models);

            // Create new digital twin
            // <CreateTwin_withHelper>
            string twinId = "myTwinID";
            var initData = new BasicDigitalTwin
            {
                Id = twinId,
                Metadata = { ModelId = "dtmi:example:Room;1" },
                // Initialize properties
                Contents =
                {
                    { "Temperature", 25.0 },
                    { "Humidity", 50.0 },
                },
            };

            // <CreateTwinCall>
            await client.CreateOrReplaceDigitalTwinAsync<BasicDigitalTwin>(twinId, initData);
            // </CreateTwinCall>
            // </CreateTwin_withHelper>
            Console.WriteLine("Twin created successfully");

            //Print twin
            Console.WriteLine("--- Printing twin details:");
            await CustomMethod_FetchAndPrintTwinAsync(twinId, client);
            Console.WriteLine("--------");

            //Update twin data
            var updateTwinData = new JsonPatchDocument();
            updateTwinData.AppendAdd("/Temperature", 30.0);
            // <UpdateTwinCall>
            await client.UpdateDigitalTwinAsync(twinId, updateTwinData);
            // </UpdateTwinCall>
            Console.WriteLine("Twin properties updated");
            Console.WriteLine();

            //Print twin again
            Console.WriteLine("--- Printing twin details (after update):");
            await CustomMethod_FetchAndPrintTwinAsync(twinId, client);
            Console.WriteLine("--------");
            Console.WriteLine();

            //Delete twin
            await CustomMethod_DeleteTwinAsync(client, twinId);
        }

        private static async Task<BasicDigitalTwin> CustomMethod_FetchAndPrintTwinAsync(string twinId, DigitalTwinsClient client)
        {
            // <GetTwin>
            BasicDigitalTwin twin;
            // <GetTwinCall>
            Response<BasicDigitalTwin> twinResponse = await client.GetDigitalTwinAsync<BasicDigitalTwin>(twinId);
            twin = twinResponse.Value;
            // </GetTwinCall>
            Console.WriteLine($"Model id: {twin.Metadata.ModelId}");
            foreach (string prop in twin.Contents.Keys)
            {
                if (twin.Contents.TryGetValue(prop, out object value))
                    Console.WriteLine($"Property '{prop}': {value}");
            }
            // </GetTwin>

            return twin;
        }

        // <DeleteTwin>
        private static async Task CustomMethod_DeleteTwinAsync(DigitalTwinsClient client, string twinId)
        {
            await CustomMethod_FindAndDeleteOutgoingRelationshipsAsync(client, twinId);
            await CustomMethod_FindAndDeleteIncomingRelationshipsAsync(client, twinId);
            try
            {
                await client.DeleteDigitalTwinAsync(twinId);
                Console.WriteLine("Twin deleted successfully");
            }
            catch (RequestFailedException ex)
            {
                Console.WriteLine($"*** Error:{ex.Message}");
            }
        }

        private static async Task CustomMethod_FindAndDeleteOutgoingRelationshipsAsync(DigitalTwinsClient client, string dtId)
        {
            // Find the relationships for the twin

            try
            {
                // GetRelationshipsAsync will throw an error if a problem occurs
                AsyncPageable<BasicRelationship> rels = client.GetRelationshipsAsync<BasicRelationship>(dtId);

                await foreach (BasicRelationship rel in rels)
                {
                    await client.DeleteRelationshipAsync(dtId, rel.Id).ConfigureAwait(false);
                    Console.WriteLine($"Deleted relationship {rel.Id} from {dtId}");
                }
            }
            catch (RequestFailedException ex)
            {
                Console.WriteLine($"*** Error {ex.Status}/{ex.ErrorCode} retrieving or deleting relationships for {dtId} due to {ex.Message}");
            }
        }

        private static async Task CustomMethod_FindAndDeleteIncomingRelationshipsAsync(DigitalTwinsClient client, string dtId)
        {
            // Find the relationships for the twin

            try
            {
                // GetRelationshipsAsync will throw an error if a problem occurs
                AsyncPageable<IncomingRelationship> incomingRels = client.GetIncomingRelationshipsAsync(dtId);

                await foreach (IncomingRelationship incomingRel in incomingRels)
                {
                    await client.DeleteRelationshipAsync(incomingRel.SourceId, incomingRel.RelationshipId).ConfigureAwait(false);
                    Console.WriteLine($"Deleted incoming relationship {incomingRel.RelationshipId} from {dtId}");
                }
            }
            catch (RequestFailedException ex)
            {
                Console.WriteLine($"*** Error {ex.Status}/{ex.ErrorCode} retrieving or deleting incoming relationships for {dtId} due to {ex.Message}");
            }
        }
        // </DeleteTwin>

    }
}

Configure project

Next, complete the following steps to configure your project code:

  1. Add the Room.json file you downloaded earlier to your project, and replace the <path-to> placeholder in the code to tell your program where to find it.

  2. Replace the placeholder <your-instance-hostname> with your Azure Digital Twins instance's host name.

  3. Add two dependencies to your project that will be needed to work with Azure Digital Twins. The first is the package for the Azure Digital Twins SDK for .NET, and the second provides tools to help with authentication against Azure.

    dotnet add package Azure.DigitalTwins.Core
    dotnet add package Azure.Identity
    

You'll also need to set up local credentials if you want to run the sample directly. The next section walks through this.

Set up local Azure credentials

This sample uses DefaultAzureCredential (part of the Azure.Identity library) to authenticate users with the Azure Digital Twins instance when you run it on your local machine. For more information on different ways a client app can authenticate with Azure Digital Twins, see Write app authentication code.

With DefaultAzureCredential, the sample will search for credentials in your local environment, like an Azure sign-in in a local Azure CLI or in Visual Studio or Visual Studio Code. For this reason, you should sign in to Azure locally through one of these mechanisms to set up credentials for the sample.

If you're using Visual Studio or Visual Studio Code to run the code sample, make sure you're signed in to that editor with the same Azure credentials that you want to use to access your Azure Digital Twins instance.

Otherwise, you can install the local Azure CLI, start a command prompt on your machine, and run the az login command to sign in to your Azure account. After you sign in, when you run your code sample, it should log you in automatically.

Run the sample

Now that you've completed setup, you can run the sample code project.

Here is the console output of the above program:

Screenshot of the console output showing that the twin is created, updated, and deleted.

Next steps

See how to create and manage relationships between your digital twins: