Model object

Model objects in Open Horizon are the metadata representation of application metadata objects. Applications are often written such that external metadata can be injected into the application in order to alter the behavior of the logic. This is notably true in the case of machine learning and AI inferencing, where the logic which analyzes a data stream uses a machine learning model to process the data to derive an analysis result. Open Horizon allows application to be structured using this metadata driven approach, by supporting the ability to deploy the application’s metadata on different lifecycle boundaries than the service (inferencing logic) which consumes the metadata. In Open Horizon, the application’s metadata is called a model, and it is represented by a model object with the JSON serialization shown below.

One aspect of the model object is the policy expressions it contains. The Open Horizon policy based, autonomous deployment capability is described here. The key to understanding model policy is remember that models are associated with services, and thus follow those services in terms of where the services are deployed. Model policy expressions are used to further constrain the deployment targets for a given model.

Use the hzn mms object new command to generate a skeleton model object file.

Following are the fields in the JSON representation of a model object:

• objectID: A unique name for a model object, created by the author of the model object. It must be unique within an Open Horizon organization. This field is required.
• objectType: A user defined name representing the type of the object. This is used to help the model object author differentiate different kinds of objects. There are no builtin types, nor does the Open Horizon runtime use this type for anything other than identifying a model object instance or group of instances. This field is required.
• destinationOrgID: The Open Horizon organization where the model object will reside. This field is required.
• destinationID: The node id (without organization prefix) where the object will be deployed. This field is optional and not recommended. You should delete this field when using destinationPolicy.
• destinationType: The Open Horizon Pattern in use by nodes where this object should be deployed. This field is optional and mutually exclusive with destinationPolicy. You should delete this field when using destinationPolicy.
• destinationList: The list of destinations as an array of pattern:nodeId pairs where the object will be deployed. This field is mutually exclusive with desinationID and destinationPolicy. You should delete this field when using destinationPolicy.
• destinationPolicy:
  • properties: Policy properties as described here that a node policy constraint can refer to.
  • constraints: Policy constraints as described here that refer to node policy properties.
  • services: A list of services that can consume the associated model object.
    • serviceName: The name of the service that will consume the model object. This is the same value as found in the url field here.
    • orgID : The organization where the service in serviceName is defined.
    • version: A version range indicating the set of service versions with which this model object is associated.
    • arch: The hardware architecture of the service in serviceName, or * to indicate any compatible architecture. This is the same value as found in the arch field here.
• expiration: A timestamp/date indicating when the object expires (it is automatically deleted). The timestamp should be provided in RFC3339 format. This field is optional.
• version: An arbitrary string value. The value is not semantically interpreted. The Open Horizon Model Management System does not keep multiple versions of an object.
• description: A long description of the model object.
• activationTime: A timestamp/date as to when this object should automatically be activated. The timestamp should be provided in RFC3339 format. This field is optional.

The following is an example of a model policy. The model object associated with this policy will be deployed on nodes where the my.company.com.services.usemodel service from serviceOrg is deployed, as long as the node properties are compatible with the model policy constraint expression. And further, that any node constraint expressions are compatible with this model’s properties:

{
  "description": "a long description of the object",
  "objectID": "uniqueString",
  "objectType": "userDefinedTypeName",
  "destinationPolicy": {
    "properties": [
      {
        "name": "prop1",
        "value": "value1",
        "type": "string"
      }
    ],
    "constraints": ["aNodeProperty == someValue"],
    "services": [
      {
        "serviceName": "my.company.com.services.usemodel",
        "orgID": "serviceOrg",
        "version": "1.0.0",
        "arch": "*",
      }
    ]
  },
  "version": "1.0.0"
}