Access Ditto Things from an Asset Administration Shell

Integrating digital representations of devices into an IT infrastructure is a recurring task in different domains and application areas. To address this challenge in Industry 4.0 scenarios along the supply chain, the community specified the Asset Administration Shell within the Industrial Digital Twin Association (IDTA) to handle all kinds of information of a physical asset over its lifecycle. Eclipse Ditto provides a backend for handling such device data as Things and takes care of a number of general tasks that are otherwise easy to be done wrong, such as handling device connectivity over different protocols or state management. Therefore, it is promising to use the benefits of Eclipse Ditto for populating an AAS infrastructure when the devices already communicate with an existing instance of Eclipse Ditto. In this post we want to share our solution and learnings from setting up an AAS infrastructure based on Eclipse Basyx and Eclipse Ditto as a source for device state. Figure 1: User-device interaction via BaSyx and Ditto Background We start with some background on the AAS and Eclipse Basyx. If you are allready familiar with both, it is safe to skip this section. Asset Administration Shell The Asset Administration Shell (AAS) is a standardization effort of the Industrial Digital Twin Association (IDTA) that originated from the Platform Industry 4.0 (I4.0) (AAS Spec Part I; AAS Spec Part II). An AAS is a digital representation of a physical asset and consists of one or more submodels. Each submodel contains a structured set of submodel elements. Submodels, as well as their submodel elements, can either be a type or an instance. The AAS metamodel defines the possible elements for modeling an AAS like Asset, AssetAdminstrationShell (AAS), Submodel (SM), SubmodelElementCollection (SMEC), Property, and SubmodelElement (SME). You can find further details here and here. A user who wants to interact with an AAS over HTTP follows the sequence of service calls depicted in Figure 2. The flow starts by requesting an AAS ID from the AAS discovery interface based on a (local) specific asset ID or a global asset ID. An example of such an asset ID is a serial number written on the device. With the AAS ID, the user retrieves the endpoint for the AAS through the AAS registry interface. The user then requests the SM ID from that AAS endpoint and uses this SM ID to get the SM endpoint from the SM Registry. From that SM endpoint, the user can request the SME, which contains the required value. Figure 2: Sequence of data flow through AAS infrastructure If you want to dig deeper into the specifics of the AAS, consult the AAS Reading Guide, which helps the interested reader to navigate through the available material. Eclipse BaSyx Eclipse BaSyx is an open-source project hosted by the Eclipse Foundation providing components to deploy an Industry 4.0 middleware. Apart from other features, Eclipse BaSyx provides several easy-to-use off-the-shelf components to realize an AAS infrastructure: AAS Server Component Registry Component DataBridge Component AAS Web UI You can pull them from Docker Hub or follow the instructions to build them yourself. In this post, we mainly work with the AAS Server Component and the Registry Component. Architectural Considerations Making Eclipse Ditto Things available in an AAS infrastructure, in our case from the Eclipse Basyx project, boils down to making Thing data available as Submodels of an AAS accessible via the AAS Interface. We see three approaches to achieve this: BaSyx AAS SM server pulls the current state from Eclipse Ditto via a wrapper around Eclipse Ditto. This approach requires the creation of a custom AAS infrastructure around Eclipse Ditto without the chance of reusing existing components of the Eclipse Basyx project. The Eclipse Ditto project followed a comparable approach to support Web of Things (WoT) definitions, which is another specification to integrate IoT devices from different contexts and align their utilized data model. Ditto now allows the generation of new Things based on a WoT Thing Description. BaSyx AAS SM server pulls the current state from Eclipse Ditto via a bridge component, which Eclipse Basyx already provides. To integrate the bridge, the BaSyx SM-server component has a delegation feature, where the user can configure an SME with an endpoint to which the server delegates incoming requests. The configured endpoint can reference the bridge that then retrieves the actual data from Ditto and applies transformation logic. Eclipse Ditto pushes the latest updates to a BaSyx SM server. For this approach, we configure Eclipse Ditto to notify the BaSyx SM server about any change to the relevant Things. During the creation of the notification message, Ditto applies a payload mapping to transform the data into the AAS format. The BaSyx SM server then stores the received submodel element and responds directly to the requests by the use

Jul 8, 2024 - 18:35
 0
Techatty All-in-1 Publishing
Techatty All-in-1 Publishing

Integrating digital representations of devices into an IT infrastructure is a recurring task in different domains and application areas. To address this challenge in Industry 4.0 scenarios along the supply chain, the community specified the Asset Administration Shell within the Industrial Digital Twin Association (IDTA) to handle all kinds of information of a physical asset over its lifecycle.

Eclipse Ditto provides a backend for handling such device data as Things and takes care of a number of general tasks that are otherwise easy to be done wrong, such as handling device connectivity over different protocols or state management. Therefore, it is promising to use the benefits of Eclipse Ditto for populating an AAS infrastructure when the devices already communicate with an existing instance of Eclipse Ditto.

In this post we want to share our solution and learnings from setting up an AAS infrastructure based on Eclipse Basyx and Eclipse Ditto as a source for device state.

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User-device interaction via AAS and IoT backend

Figure 1: User-device interaction via BaSyx and Ditto

Background

We start with some background on the AAS and Eclipse Basyx. If you are allready familiar with both, it is safe to skip this section.

Asset Administration Shell

The Asset Administration Shell (AAS) is a standardization effort of the Industrial Digital Twin Association (IDTA) that originated from the Platform Industry 4.0 (I4.0) (AAS Spec Part I; AAS Spec Part II).

An AAS is a digital representation of a physical asset and consists of one or more submodels. Each submodel contains a structured set of submodel elements. Submodels, as well as their submodel elements, can either be a type or an instance. The AAS metamodel defines the possible elements for modeling an AAS like Asset, AssetAdminstrationShell (AAS), Submodel (SM), SubmodelElementCollection (SMEC), Property, and SubmodelElement (SME). You can find further details here and here.

A user who wants to interact with an AAS over HTTP follows the sequence of service calls depicted in Figure 2. The flow starts by requesting an AAS ID from the AAS discovery interface based on a (local) specific asset ID or a global asset ID. An example of such an asset ID is a serial number written on the device. With the AAS ID, the user retrieves the endpoint for the AAS through the AAS registry interface. The user then requests the SM ID from that AAS endpoint and uses this SM ID to get the SM endpoint from the SM Registry. From that SM endpoint, the user can request the SME, which contains the required value.

Sequence of data flow through AAS infrastructure

Figure 2: Sequence of data flow through AAS infrastructure

If you want to dig deeper into the specifics of the AAS, consult the AAS Reading Guide, which helps the interested reader to navigate through the available material.

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Eclipse BaSyx

Eclipse BaSyx is an open-source project hosted by the Eclipse Foundation providing components to deploy an Industry 4.0 middleware. Apart from other features, Eclipse BaSyx provides several easy-to-use off-the-shelf components to realize an AAS infrastructure:

You can pull them from Docker Hub or follow the instructions to build them yourself.

In this post, we mainly work with the AAS Server Component and the Registry Component.

Architectural Considerations

Making Eclipse Ditto Things available in an AAS infrastructure, in our case from the Eclipse Basyx project, boils down to making Thing data available as Submodels of an AAS accessible via the AAS Interface.

We see three approaches to achieve this:

  • BaSyx AAS SM server pulls the current state from Eclipse Ditto via a wrapper around Eclipse Ditto. This approach requires the creation of a custom AAS infrastructure around Eclipse Ditto without the chance of reusing existing components of the Eclipse Basyx project. The Eclipse Ditto project followed a comparable approach to support Web of Things (WoT) definitions, which is another specification to integrate IoT devices from different contexts and align their utilized data model. Ditto now allows the generation of new Things based on a WoT Thing Description.
  • BaSyx AAS SM server pulls the current state from Eclipse Ditto via a bridge component, which Eclipse Basyx already provides. To integrate the bridge, the BaSyx SM-server component has a delegation feature, where the user can configure an SME with an endpoint to which the server delegates incoming requests. The configured endpoint can reference the bridge that then retrieves the actual data from Ditto and applies transformation logic.
  • Eclipse Ditto pushes the latest updates to a BaSyx SM server. For this approach, we configure Eclipse Ditto to notify the BaSyx SM server about any change to the relevant Things. During the creation of the notification message, Ditto applies a payload mapping to transform the data into the AAS format. The BaSyx SM server then stores the received submodel element and responds directly to the requests by the users.
Push approach sequence

Figure 3: Push approach sequence

We follow the push approach here because it treats the AAS infrastructure as a blackbox and almost all configuration happens within Eclipse Ditto.

Mapping of Data Models

Eclipse Ditto and Eclipse Basyx work with different data structures and conceptual elements to represent device and asset data. Since we want to convert between these data models, we need to come up with a mapping between them.

Eclipse Ditto Asset Administration Shell
Namespace Asset Administration Shell
Thing
Features Submodel
Property Submodel Element
Attribute Submodel Element

Table 1: Concept mapping from Eclipse Ditto to the AAS

We map a Ditto Namespace to a single AAS. An AAS holds multiple SMs, and not all of these SMs necessarily have counterparts in Ditto. We thus treat a Thing as an opaque concept and do not define an explicit mapping for a Thing but map each feature to one SM. property and Attribute are mapped to SMEs.

By that, it is possible to have more than one Thing organized in one AAS. This can especially be useful if an AAS organizes complex equipment with different sensors and actuators, which belong together but are organized in multiple Things.

Integration Steps

With the more theoretical details completed, we can now turn to the actual implementation and describe what is required to integrate Eclipse Ditto into an AAS infrastructure of Eclipse BaSyx.

Prerequisites

  1. Running instance of Eclipse Ditto
  2. Running instance of Eclipse BaSyx AAS Server
  3. Running instance of Eclipse BaSyx AAS Registry

Those three instances must be available and a network connection must exist between them. In the code snippets below, we use placeholders for the URLs of Ditto as well as BaSyx. So, you need to replace , , with the proper URLs in your environment.

For our setup, we used version 3.0.1 for Eclipse Ditto and version 1.4.0 for Eclipse BaSyx. Please note that the Ditto demo instance, does not work for the described setup and requests because it does not allow to directly invoke the /devops endpoints through which we later configure connections.

Payload Mappers from Ditto to BaSyx

Let us assume a device with a sensor named machine:sensor that is capable of measuring temperature values. This device may send sensor data to an Eclipse Ditto instance as a Ditto Protocol message Ditto Protocol message:

{
  "topic": "machine/sensor/things/twin/commands/modify",
  "headers": {},
  "path": "/features/temperature/properties/value",
  "value": 46
}

Listing 1: Ditto Protocol message for the Thing machine:senor

If the device uses another message format, you can find more details on how to map it to a Ditto Protocol message.

After an update to a Thing, we want Ditto to map the information to an AAS-conforming representation and forward this via an outbound connection to an AAS server. The task in Eclipse Ditto is to define payload mappers for these transformations in accordance with the mapping from Mapping of Data Models. Ditto allows the usage of JavaScript to create the mappers. We thus configure connections in Ditto to the BaSyx components, where we filter for the relevant changes to a Thing and then trigger the respective mapper.

We need to implement the following mappers:

  • Creation of an AAS triggered by creation of new namespaces
  • Creation of a SM triggered by creation of feature
  • Creation and update of an SME triggered by creation and modification of a property

Map from Thing Creation to AAS Creation

The next snippet performs a mapping from a Thing to an AAS. It gets executed every time a Thing is created.

function mapFromDittoProtocolMsg(
  namespace,
  name,
  group,
  channel,
  criterion,
  action,
  path,
  dittoHeaders,
  value,
  status,
  extra
) {
  let headers = dittoHeaders;
  let textPayload = JSON.stringify({
    conceptDictionary: [],
    identification: {
      idType: 'Custom',
      id: namespace
    },
    idShort: namespace,
    dataSpecification: [],
    modelType: {
      name: 'AssetAdministrationShell'
    },
    asset: {
      identification: {
        idType: 'Custom',
        id: namespace + '-asset'
      },
      idShort: namespace + '-asset',
      kind: 'Instance',
      dataSpecification: [],
      modelType: {
        name: 'Asset'
      },
      embeddedDataSpecifications: []
    },
    embeddedDataSpecifications: [],
    views: [],
    submodels: []
  });
  let bytePayload = null;
  let contentType = 'application/json';
  return Ditto.buildExternalMsg(
    headers, // The external headers Object containing header values
    textPayload, // The external mapped String
    bytePayload, // The external mapped byte[]
    contentType // The returned Content-Type
  );
}

Listing 2: Payload mapping that creates a new AAS if a new Thing appears

As we map the Thing namespace to an AAS we only use the namespace, which is the first part of the ID of a Thing. For example machine in our machine:sensor example Thing (Listing 1). More precisely, the mapping creates a representation of an AAS with the ID namespace and returns a new message with this text as payload. The Ditto connectivity service then runs the mapping and pushes the new message to the BaSyx AAS server to create the described AAS. For example, whenever a Thing with the ID machine:sensor is created, an AAS with the ID machine will be created.

Map from Feature creation to Submodel creation

The next mapper creates an AAS submodel and will be executed every time a new feature is created for a Thing.

function mapFromDittoProtocolMsg(
  namespace,
  name,
  group,
  channel,
  criterion,
  action,
  path,
  dittoHeaders,
  value,
  status,
  extra
) {
  
  let feature_id = path.split('/').slice(2);
  let headers = dittoHeaders;
  let textPayload = JSON.stringify(
    {
      parent: {
        keys: [
          {
            idType: 'Custom',
            type: 'AssetAdministrationShell',
            value: namespace,
            local: true
          }
        ]
      },
      identification: {
        idType: 'Custom',
        id: name+'_'+feature_id
      },
      idShort: name+'_'+feature_id,
      kind: 'Instance',
      dataSpecification: [],
      modelType: {
        name: 'Submodel'
      },
      embeddedDataSpecifications: [],
      submodelElements: []
    }

  );
  let bytePayload = null;
  let contentType = 'application/json';
  return Ditto.buildExternalMsg(
    headers, // The external headers Object containing header values
    textPayload, // The external mapped String
    bytePayload, // The external mapped byte[]
    contentType // The returned Content-Type
  );
}

Listing 3: Payload mapping that creates a new AAS submodel if a new Feature appears

Besides namespace, this mapper uses the parameters name and path from the Ditto Protocol message. The name represents the second part of the Thing-ID, e.g., sensor from our machine:sensor example Thing (Listing 1). The path describes the part of the Thing whose change triggered the processed Ditto Protocol message. It may include the feature ID of the Thing or the whole path of the affected property of the Thing, but it could be only / after the creation of a Thing. In our example message above, the path is /features/temperature/properties/value.

The mapping function extracts the ID of the feature from the parameter path and uses this together with the name of the Thing to build the ID of the corresponding AAS submodel. For example, whenever the feature temperature of a Thing called machine:sensor is created, an AAS submodel with the ID sensor_temperature in the AAS machine will be created.

Similarly to the AAS creation mapping, the listed function returns a new message with a custom text payload. Below, we will create a connection so that this payload gets pushed to the BaSyx AAS server to trigger the creation of an AAS submodel there.

Map from Property Update to Submodel Update

The next mapper creates an AAS submodel element. we use it in the connection for every modification of a property in a Thing.

function mapFromDittoProtocolMsg(
  namespace,
  name,
  group,
  channel,
  criterion,
  action,
  path,
  dittoHeaders,
  value,
  status,
  extra
) {
  let property_id = path.split('/').slice(3).join('_');
  let feature_id = path.split('/').slice(2,3);
  let headers = dittoHeaders;
  let dataType = typeof value;
  dataType = mapDataType(dataType)

  function mapDataType(dataType) {
    switch (dataType) {
        case 'undefined':
        return 'Undefined';
        case 'boolean':
        return 'boolean';
        case 'number':
        return 'int';
        case 'string':
        return 'string';
        case 'symbol':
        return 'Symbol';
        case 'bigint':
        return 'BigInt';
        case 'object':
        return 'string';
        case 'function':
        return 'Function';
        default:
        return 'Unknown';
    }
  }
  let textPayload = JSON.stringify(
  {
    parent: {
      keys: [
        {
          idType: 'Custom',
          type: 'Submodel',
          value: name+'_'+feature_id,
          local: true
        }
      ]
    },
    idShort: property_id,
    kind: 'Instance',
    valueType: dataType,
    modelType: {
      name: 'Property'
    },
    value: value
  }
  );
  let bytePayload = null;
  let contentType = 'application/json';
  return Ditto.buildExternalMsg(
    headers, // The external headers Object containing header values
    textPayload, // The external mapped String
    bytePayload, // The external mapped byte[]
    contentType // The returned Content-Type
  );
}

Listing 4: Payload mapping that modifies an AAS submodel element if a property is changed

The mapper extracts the feature_id and the property_id from the path, which is only possible if the parameter path includes the property_id. So, in the configuration of the connection, we have to ensure that this mapper only runs for the right messages. Moreover, we can access the value of the modified property, which will be set as value in the submodel element from the textPayload output.

For example, if a message updates the path: /features/temperature/properties/value in the Thing machine:sensor, the submodel element with the ID properties_value in the submodel sensor_temperature will be updated with the new temperature as value.

We update a submodel element instead of the whole submodel if an existing Thing changes because the mapper only has access to the changed property of the Thing and no information about the other properties. Therefore, submodel elements, which may already be part of the submodel due to previous updates, would implicitly be dropped. With our approach, we preserve the existing properties and only modify the updated properties.

Create a Connection to the BaSyx AAS Server

To apply the introduced mappers, we configure a new Ditto connection to a BaSyx AAS server. The listings below show the respective HTTP calls using curl to configure this connection.

The JavaScript mappers from above are part of piggybackCommand.connection.mappingDefinitions in mappingforShell, mappingforSubmodel and mappingforSubmodelElement.

In the example, we use the placeholder for the used Ditto instance. You need to adjust to the valid URL of your environment. We assume you have access rights to the Ditto Devops Commands credentials in the used instance (username: devops, password: `foobar is the default).

You can change the password by setting the environment variable DEVOPS_PASSWORD in the gateway service.

Alternatively, an already existing password can be obtained and stored as an environment variable using the following command:

export DEVOPS_PWD=$(kubectl --namespace ditto get secret my-ditto-gateway-secret -o jsonpath="{.data.devops-password}" | base64 --decode)

Please be aware that this command assumes Ditto has been deployed within a namespace ditto.

Finally, you adjust the parameter piggybackCommand.connection.uri with the URL of the running BaSyx server to which Ditto should have network connectivity.

As HTTP requires us to replace certain characters for proper processing, we encode the payload by escaping certain characters and removing the line breaks. We replaced newlines with \n and ' with '"'.

curl -X POST -u devops:foobar -H 'Content-Type: application/json' --data-binary '{
    "targetActorSelection": "/system/sharding/connection",
    "headers": {
      "aggregate": false
    },
    "piggybackCommand": {
      "type": "connectivity.commands:createConnection",
      "connection": {
        "id": "basyxserver-http-connection",
        "connectionType": "http-push",
        "connectionStatus": "open",
        "uri": ":4001",
        "failoverEnabled": true,
        "mappingDefinitions": {
          "mappingforShell": {
            "mappingEngine": "JavaScript",
            "options": {
              "outgoingScript": "function mapFromDittoProtocolMsg(namespace, name, group, channel, criterion, action, path, dittoHeaders, value, status, extra) {\n  let headers = dittoHeaders;\n  let textPayload = JSON.stringify({\n    conceptDictionary: [],\n    identification: {\n      idType: '"'Custom'"',\n      id: namespace\n    },\n    idShort: namespace,\n    dataSpecification: [],\n    modelType: {\n      name: '"'AssetAdministrationShell'"'\n    },\n    asset: {\n      identification: {\n        idType: '"'Custom'"',\n        id: namespace + '"'-asset'"'\n      },\n      idShort: namespace + '"'-asset'"',\n      kind: '"'Instance'"',\n      dataSpecification: [],\n      modelType: {\n        name: '"'Asset'"'\n      },\n      embeddedDataSpecifications: []\n    },\n    embeddedDataSpecifications: [],\n    views: [],\n    submodels: []\n  });\n  let bytePayload = null;\n  let contentType = '"'application/json'"';\n  return Ditto.buildExternalMsg(headers, textPayload, bytePayload, contentType);}"            
            }
          },
          "mappingforSubmodel": {
            "mappingEngine": "JavaScript",
            "options": {
                "outgoingScript": "function mapFromDittoProtocolMsg(namespace, name, group, channel, criterion, action, path, dittoHeaders, value, status, extra) {\n  \n  let feature_id = path.split('"'/'"').slice(2);\n  let headers = dittoHeaders;\n  let textPayload = JSON.stringify(\n    {\n      parent: {\n        keys: [\n          {\n            idType: '"'Custom'"',\n            type: '"'AssetAdministrationShell'"',\n            value: namespace,\n            local: true\n          }\n        ]\n      },\n      identification: {\n        idType: '"'Custom'"',\n        id: name+'"'_'"'+feature_id\n      },\n      idShort: name+'"'_'"'+feature_id,\n      kind: '"'Instance'"',\n      dataSpecification: [],\n      modelType: {\n        name: '"'Submodel'"'\n      },\n      embeddedDataSpecifications: [],\n      submodelElements: []\n    }\n\n  );\n  let bytePayload = null;\n  let contentType = '"'application/json'"';\n  return Ditto.buildExternalMsg(headers, textPayload, bytePayload, contentType);}"
            }
          },
          "mappingforSubmodelElement": {
            "mappingEngine": "JavaScript",
            "options": {
              "outgoingScript": "function mapFromDittoProtocolMsg(namespace, name, group, channel, criterion, action, path, dittoHeaders, value, status, extra) {\n  let property_id = path.split('"'/'"').slice(3).join('"'_'"');\n  let feature_id = path.split('"'/'"').slice(2,3);\n  let headers = dittoHeaders;\n  let dataType = typeof value;\n  dataType = mapDataType(dataType)\n\n  function mapDataType(dataType) {\n    switch (dataType) {\n        case '"'undefined'"':\n        return '"'Undefined'"';\n        case '"'boolean'"':\n        return '"'boolean'"';\n        case '"'number'"':\n        return '"'int'"';\n        case '"'string'"':\n        return '"'string'"';\n        case '"'symbol'"':\n        return '"'Symbol'"';\n        case '"'bigint'"':\n        return '"'BigInt'"';\n        case '"'object'"':\n        return '"'string'"';\n        case '"'function'"':\n        return '"'Function'"';\n        default:\n        return '"'Unknown'"';\n    }\n  }\n  let textPayload = JSON.stringify(\n  {\n    parent: {\n      keys: [\n        {\n          idType: '"'Custom'"',\n          type: '"'Submodel'"',\n          value: name+'"'_'"'+feature_id,\n          local: true\n        }\n      ]\n    },\n    idShort: property_id,\n    kind: '"'Instance'"',\n    valueType: dataType,\n    modelType: {\n      name: '"'Property'"'\n    },\n    value: value\n  }\n  );\n  let bytePayload = null;\n  let contentType = '"'application/json'"';\n  return Ditto.buildExternalMsg(headers, textPayload, bytePayload, contentType);}"
            }
          }
        },
        "sources": [],
        "targets": [
          {
            "address": "PUT:/aasServer/shells/{{ thing:namespace }}",
            "headerMapping": {
              "content-type": "{{ header:content-type }}"
            },
            "authorizationContext": ["nginx:ditto"],
            "topics": [
              "_/_/things/twin/events?filter=and(in(topic:action,'"'created'"'),eq(resource:path,'"'/'"'))"
            ],
            "payloadMapping": [
              "mappingforShell"
            ]
          },
          {
            "address": "PUT:/aasServer/shells/{{ thing:namespace }}/aas/submodels/{{ thing:name }}_{{ resource:path | fn:substring-after('"'/features/'"') }}",
            "headerMapping": {
              "content-type": "{{ header:content-type }}"
            },
            "authorizationContext": ["nginx:ditto"],
            "topics": [
              "_/_/things/twin/events?filter=and(in(topic:action,'"'created'"'),not(eq(resource:path,'"'/features'"')),like(resource:path,'"'/features*'"'),not(like(resource:path,'"'*properties*'"')))"
            ],
            "payloadMapping": [
              "mappingforSubmodel"
            ]
          },
          {
            "address": "PUT:/aasServer/shells/{{ thing:namespace }}/aas/submodels/{{ thing:name }}_{{ resource:path | fn:substring-after('"'/features/'"') | fn:substring-before('"'/properties'"') }}/submodel/submodelElements/properties_{{ resource:path | fn:substring-after('"'/properties/'"') | fn:replace('"'/'"','"'_'"') }}",
            "headerMapping": {
              "content-type": "{{ header:content-type }}"
            },
            "authorizationContext": ["nginx:ditto"],
            "topics": [
              "_/_/things/twin/events?filter=and(in(topic:action,'"'modified'"'),not(eq(resource:path,'"'/features'"')),like(resource:path,'"'/features*'"'),like(resource:path,'"'*properties*'"'),not(like(resource:path,'"'*properties'"')))"
            ],
            "payloadMapping": [
              "mappingforSubmodelElement"
            ]
          }
        ]
      }
    }
  }' /devops/piggyback/connectivity

Listing 5: Request to add a new Connection to a Ditto instance

When Ditto established the connection and our payload mappings work, it returns a successful HTTP response and otherwise an error message.

Without any further means, the payload mappings defined in piggybackCommand.mappingDefinition and set in piggybackCommand.targets would get executed for all changes to a Thing. To prevent this, we use filtering with RQL expressions to make sure that our payload mappings are only executed for the correct messages. For example, the filter:

_/_/things/twin/events?filter=and(in(topic:action,'"'created'"'),eq(resource:path,'"'/'"'))

before mappingforShell in piggybackCommands.targets[0].topics[0] makes sure that it only triggers for messages, which create a Thing.

Another filter for mappingForSubmodel in pigybackCommands.targets[1].topics[0] makes sure, that the parameter path contains a feature and not a property:

"_/_/things/twin/events?filter=and(in(topic:action,'"'created'"'),not(eq(resource:path,'"'/features'"')),like(resource:path,'"'/features*'"'),not(like(resource:path,'"'*properties*'"')))"

Setup Connection to an BaSyx AAS Registry

Within an AAS environment it is required that AAS are discoverable via an AAS registry. We make an AAS discoverable by adding an entry for that AAS into the AAS registry for a new Thing. In our setup we achieve this through the definition of a new connection between Eclipse Ditto and the BaSyx AAS Registry with a respective payload mapping.

function mapFromDittoProtocolMsg(
  namespace,
  name,
  group,
  channel,
  criterion,
  action,
  path,
  dittoHeaders,
  value,
  status,
  extra
) {
  let headers = dittoHeaders;
  let textPayload = JSON.stringify({
    endpoints: [
        {
            address: ':4001/aasServer/shells/' + namespace + '/aas',
            type: 'http'
        }
    ],
    modelType: {
        name: 'AssetAdministrationShellDescriptor'
    },
    identification: {
        idType: 'Custom',
        id: namespace
},
    idShort: namespace,
      asset: {
          identification: {
              idType: 'Custom',
              id: namespace + '-asset'
          },
          idShort: namespace + '-asset',
          kind: 'Instance',
          dataSpecification: [],
          modelType: {
              name: 'Asset'
          },
          embeddedDataSpecifications: []
      },
      submodels: []
  });
  let bytePayload = null;
  let contentType = 'application/json';
  return Ditto.buildExternalMsg(
    headers, // The external headers Object containing header values
   textPayload, // The external mapped String
   bytePayload, // The external mapped byte[]
    contentType // The returned Content-Type
);
}

Listing 6: Snippet to add a new AAS Registry entry for an AAS

As introduced in Mapping of Data Models, we map a namespace in Ditto to an AAS. The new entry in the BaSyx Registry has to contain the endpoint of the BaSyx AAS server, which hosts the new AAS. You find this in the script-payload in the variable endpoints.address. So you need to adapt this value in the following HTTP request to the address of the BaSyx ASS server that you are using and that was configured in the connection between Ditto and the BaSyx AAS Server.

With this mapping, it is now possible to configure a new connection from Ditto to a BaSyx AAS registry through the following HTTP request:

curl -X POST -u devops:foobar -H 'Content-Type: application/json' --data-binary '{
    "targetActorSelection": "/system/sharding/connection",
    "headers": {
      "aggregate": false
    },
    "piggybackCommand": {
      "type": "connectivity.commands:createConnection",
      "connection": {
        "id": "basyxregistry-http-connection",
        "connectionType": "http-push",
        "connectionStatus": "open",
        "uri": ":4000",
        "failoverEnabled": true,
        "mappingDefinitions": {
          "mappingforShell": {
            "mappingEngine": "JavaScript",
            "options": {
              "outgoingScript": "function mapFromDittoProtocolMsg(namespace, name, group, channel, criterion, action, path, dittoHeaders, value, status, extra) {\n  let headers = dittoHeaders;\n  let textPayload = JSON.stringify({\n    endpoints: [\n        {\n            address: '"':4001/aasServer/shells/'"' + namespace + '"'/aas'"',\n            type: '"'http'"'\n        }\n    ],\n    modelType: {\n        name: '"'AssetAdministrationShellDescriptor'"'\n    },\n    identification: {\n        idType: '"'Custom'"',\n        id: namespace\n},\n    idShort: namespace,\n      asset: {\n          identification: {\n              idType: '"'Custom'"',\n              id: namespace + '"'-asset'"'\n          },\n          idShort: namespace + '"'-asset'"',\n          kind: '"'Instance'"',\n          dataSpecification: [],\n          modelType: {\n              name: '"'Asset'"'\n          },\n          embeddedDataSpecifications: []\n      },\n      submodels: []\n  });\n  let bytePayload = null;\n  let contentType = '"'application/json'"';\n  return Ditto.buildExternalMsg(headers, textPayload, bytePayload, contentType);}"
            }
          }
        },
        "sources": [],
        "targets": [
          {
            "address": "PUT:/registry/api/v1/registry/{{ thing:namespace }}",
            "headerMapping": {
              "content-type": "{{ header:content-type }}"
            },
            "authorizationContext": ["nginx:ditto"],
            "topics": [
              "_/_/things/twin/events?filter=and(in(topic:action,'"'created'"'),eq(resource:path,'"'/'"'))"
            ],
            "payloadMapping": [
              "mappingforShell"
            ]
          }
        ]
      }
    }
  }' /devops/piggyback/connectivity

Listing 7: Request to add a new Connection to a Ditto instance

We list the JavaScript mapper in piggybackCommand.connection.mappingDefinitions.mappingForShell.options.outgoingScript and reference it as mappingForShell in piggybackCommand.connection.targets[0].payloadMapping. The address of the BaSyx AAS registry is configured in the parameter piggybackCommand.connection.uri.

As filter, to make sure that our mapper function only triggers after the creation of new Thing, we use:

"_/_/things/twin/events?filter=and(in(topic:action,'"'created'"'),eq(resource:path,'"'/'"'))"

Since the registry uses the AAS server endpoint as a base to also get access to all submodels and submodel elements from the same AAS, it is enough to register the AAS endpoint.

Test the Connection

We now configured all required connections in Ditto and can test our setup. All configured mappers trigger through changes to a Thing, so we begin by creating a Thing.

We again refer to the used Ditto instance through the placeholder , which you need to adapt to the URL of your Ditto instance.

Creating a Thing in Eclipse Ditto

Setup a common policy

To define authorization information to be used by the Things, we first create a policy with the policy-id machine:my-policy.

POLICY_ID=machine:my-policy

curl -i -X PUT -u ditto:ditto -H 'Content-Type: application/json' --data '{
  "entries": {
    "DEFAULT": {
      "subjects": {
        "{{ request:subjectId }}": {
           "type": "Ditto user authenticated via nginx"
        }
      },
      "resources": {
        "thing:/": {
          "grant": ["READ", "WRITE"],
          "revoke": []
        },
        "policy:/": {
          "grant": ["READ", "WRITE"],
          "revoke": []
        },
        "message:/": {
          "grant": ["READ", "WRITE"],
          "revoke": []
        }
      }
    }
  }
}' /api/2/policies/$POLICY_ID

Listing 8: Demo Policy Definition

You will get a 201 Created response, if the policy creation concluded successfuly. In the subsequent steps, we use the policy-id machine:my-policy to refer to the created policy.

Create a Thing

The next step is to create an actual Thing. We use the namespace and name machine:my-policy and policy-id machine:my-policy here:

NAMESPACE=machine
NAME=sensor
DEVICE_ID=$NAMESPACE:$NAME

curl -i -X PUT -u ditto:ditto -H 'Content-Type: application/json' --data '{
  "policyId": "'$POLICY_ID'"
}' /api/2/things/$DEVICE_ID

Listing 9: Request to add the Demo Policy to a Ditto instance ($POLICY_ID refers to Listing 8)

Again, a successful creation returns a 201 Created response.

We earlier configured two connections to trigger a mapper on the create event of a Thing. This should push a new AAS to the AAS server and a reference to that AAS in the AAS registry.

You can check whether the execution of the scripts was successful by requesting the shell at the AAS server:

curl -X GET :4001/aasServer/shells

which should return the following result

[{"modelType":{"name":"AssetAdministrationShell"},"idShort":"machine","identification":{"idType":"Custom","id":"machine"},"dataSpecification":[],"embeddedDataSpecifications":[],"submodels":[{"keys":[{"type":"AssetAdministrationShell","local":true,"value":"machine","idType":"Custom"},{"type":"Submodel","local":true,"value":"sensor_temperature","idType":"Custom"}]}],"asset":{"keys":[{"type":"Asset","local":true,"value":"machine-asset","idType":"Custom"}],"identification":{"idType":"Custom","id":"machine-asset"},"idShort":"machine-asset","kind":"Instance","dataSpecification":[],"modelType":{"name":"Asset"},"embeddedDataSpecifications":[]},"views":[],"conceptDictionary":[]}]

In addition, the request to the AAS registry:

curl -X GET :4000/registry/api/v1/registry

should return:

[{"modelType":{"name":"AssetAdministrationShellDescriptor"},"endpoints":[{"address":":4001/aasServer/shells/machine/aas","type":"http"}],"identification":{"idType":"Custom","id":"machine"},"idShort":"machine","asset":{"identification":{"idType":"Custom","id":"machine-asset"},"idShort":"machine-asset","kind":"Instance","dataSpecification":[],"modelType":{"name":"Asset"},"embeddedDataSpecifications":[]},"submodels":[]}]

At this point, the newly created Thing has no features, properties, or attributes yet. So let us populate that Thing.

Create a feature for the Thing

Next, we create a feature for the Thing to contain a property with the data of a temperature sensor.

FEATURE_ID=temperature

curl -X PUT -u ditto:ditto -H 'Content-Type: application/json' --data-binary '{
  "properties": {
    "value": null
  }
}' /api/2/things/$DEVICE_ID/features/$FEATURE_ID

Listing 10: Request to add a feature to the demo Thing (variables refer to previous Listings)

The feature creation triggers the mapper (mappingforSubmodel) to create a corresponding Submodel in the previously created AAS.

To check if this was successful, we request the expected submodel:

curl -X GET :4001/aasServer/shells/$NAMESPACE/aas/submodels/${NAME}_${FEATURE_ID}/submodel

which should result in the following response:

{"parent":{"keys":[{"idType":"Custom","type":"AssetAdministrationShell","value":"machine","local":true}]},"identification":{"idType":"Custom","id":"sensor_temperature"},"idShort":"sensor_temperature","kind":"Instance","dataSpecification":[],"modelType":{"name":"Submodel"},"embeddedDataSpecifications":[],"submodelElements":[]}

Updating a Thing

After we have successfully created a Thing, we can check if the update of a property works as well by executing:

curl -i -X PUT -u ditto:ditto -H "content-type: application/json" --data-binary '46' /api/2/things/$DEVICE_ID/features/$FEATURE_ID/properties/value

Again, we check if our change was successful:

curl -u ditto:ditto -w '\n' /api/2/things/$DEVICE_ID

and expect:

{"thingId":"machine:sensor","policyId":"machine:my-policy","features":{"temperature":{"properties":{"value":46}}}}

If the property creation was successful, then the mapping mappingforSubmodelElement should trigger. To verify that the Submodel was updated, call:

curl -X GET :4001/aasServer/shells/$NAMESPACE/aas/submodels/${NAME}_${FEATURE_ID}/submodel/submodelElements/properties_value

This should lead to the response:

{"parent":{"keys":[{"idType":"Custom","type":"Submodel","value":"sensor_temperature","local":true}]},"idShort":"properties_value","kind":"Instance","valueType":"int","modelType":{"name":"Property"},"value":46}

Here, we see that we are able to access the sensor data of the device through the AAS Submodel API via Eclipse BaSyx.

As an alternative to plain Json responses, you can use one of the UI-tools provided by the AAS community, like the AAS Web UI.

AAS Dashboard

Figure 4: BaSyx AAS Web UI

Summary

In this post, we present our approach for making Ditto Things available in an AAS. We defined a mapping concept between Things and AAS. To apply the mapping concept, we created connections with mappers from Ditto to a BaSyx AAS server and a BaSyx AAS registry. Afterwards, we tested the connections with an example Thing and data from a sensor.

Our example of integrating Ditto Things into an AAS environment shows, how the capbilities of Ditto, such as custom mappers, filters etc, render it a useful tool to integrate device states into various environments. We discussed the integration into AAS but believe a similar approach could be applied in other domains as well.



Milena Jäntgen, Sven Erik Jeroschewski and Max Grzanna contributed to this post.

Ditto Eclipse Ditto™ is a technology in the IoT implementing a software pattern called “digital twins”. A digital twin is a virtual, cloud based, representation of his real world counterpart (real world “Things”, e.g. devices like sensors, smart heating, connected cars, smart grids, EV charging stations, …). The technology mirrors potentially millions and billions of digital twins residing in the digital world with physical “Things”. This simplifies developing IoT solutions for software developers as they do not need to know how or where exactly the physical “Things” are connected.
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