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UDMI / Docs / Specs / Metadata

Metadata Description File

A device's metadata.json is a description about the device: a specification about how the device should be configured and expectations about what the device should be doing. It is used to provide the basic information for registering devices in a IoT Core registry, generation of other template files (e.g. config block) associated with the device, and as a means for runtime validation of what the device is actually sending.

The metadata.json files are stored in a devices/{device_id} directory with an expected 1:1 mapping between device directory and device entry in a IoT Core registry.

System Tooling

There are three main sets of tools that rely on the metadata.json file, all found in the UDMI bin/ directory.

  • genkeys: Generates public/private device key pairs (optional as needed).
  • registrar: Validates metadata files and can (optionally) register devices.
  • validator: Validates live data stream from devices.

Output Files

The various tools will generate some output files in the same devices/ directory:

  • rsa_*: Device public/private key files (genkeys tool).
  • metadata_norm.json: Normalized version of the metadata.json file (registrar tool).
  • generated_config.json: Default device IoT Core config block (registrar tool).
  • errors.map: Detailed error file (registrar tool).

Metadata Structure

The structure of the metadata file is shown in the 🧬metadata schema

Metadata Registration and Validation

Using UDMI on a project entails not only the base device implementations, but also properly registering and validating device configuration. The registrar tool and validator tool provide a means to configure and check site installations, respectively.

Example

This working example shows how a typical metadata file is constructed.