IBAZ: Mappings and Constraints

Overview

There are six primary components used in a system using IoT Bridge. There are:

• Edge Gateways publishing Sparkplug based MQTT data
  • Our examples will use Ignition with MQTT Transmission for the Edge Gateway
• An MQTT Server
  • This could be any v3.1.1 compliant MQTT Server and our examples will use Cirrus Link Chariot MQTT Server.
• IoT Bridge for Azure (IBAZ)
• Azure Digital Twin (ADT)
• Azure Event Hub
• Azure Data Explorer

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There are some translations that need to take place between the components and these platforms have different capabilities that result in some limitations in how an Edge Gateway can be configured. For example, UDTs in Ignition support more data types that Azure Digital Twin (ADT) does. As a result, use of data types in Ignition must be limited to those supported by Azure Digital Twin (ADT) in order for data to properly show up and be updated in Azure Data Explorer. 

Mappings

Ignition and Azure Digital Twin use different terminology for similar constructs. Those definitions are below.

• An Ignition 'UDT Definition' is mapped to an ADT 'Asset Model'.
• An Ignition 'UDT Instance' is mapped to a ADT 'Asset'.
• Ignition 'UDT parameters' are mapped to 'ADT Attributes'.
• Ignition 'UDT member tags' are mapped to 'ADT Measurements'.
• Transform, Metric, and Hierarchy definitions in ADT are not used by IBAZ.

Constraints and Limitations

Supported Data Types

Azure Digital Twin only supports Booleans, Integers, Doubles, and Strings. As a result, this is the list of data types in Ignition that are supported for consumption into Azure Digital Twin.

• Boolean
• Byte
  • Will be up-casted to an Integer in ADT
• Short
  • Will be up-casted to an Integer in ADT
• Integer
• Float
  • Will be up-casted to an Double in ADT
• Double
• String

Any non-supported data type will be converted to a String in ADT and the measurement value for any instance will show an error with a message similar to "Long is not a valid datatype"

User Defined Types (UDTs)

• Azure Digital Twin Asset Models have a limit of 200 Attributes and/or Measurements. Therefore UDTs with more than 200 Parameters or member tags will result in the Model not being created in Azure.
• UDT Tag and Property names that result in creating Azure Digital Twin Measurements and Attributes name, you must follow the regex expression pattern
  • ^[a-zA-Z0-9_-]+$ (for more information on regex expression patterns go to https://regexr.com)
• UDT parameter 'Integers' in Ignition are actually Long values. As a result, UDT parameters of type Integer are not supported at this time.

Nested/Hierarchical User Defined Types (UDTs)

These are not supported currently in IoT Bridge. Azure Digital Twin allows Asset Models to have one or more child Asset Models. Ignition supports UDTs having children UDTs as well as UDTs referencing a parent UDT. However, these hierarchical relationships will not be maintained by IBAZ. Support for simple hierarchies as supported by Azure Digital Twin will be added in a future version of IoT Bridge.

Azure Digital Twin Limits and Quotas

Azure Digital Twin has limits and quotas on many different aspects of asset model counts, asset counts, number or attributes per model, etc. For details on those limits see this document.