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Session Metamodel#

The metamodel1 enables the service to describe what session properties are available and what values they can take.

Info

The Session Service generates a metamodel from session properties.

There is scope for still-deeper integration for implementations that manage complex simulation models or perform federated queries into other systems.

For example:

curl -H "Accept: application/json" "http://localhost:2650/rta/v2/session-metamodel" 

{
    "details": {
        "label": "Details",
        "properties": {
            "Engineer": {
                "type": "string",
                "constraints": {
                    "values": [
                        "Joe",
                        "Robert"
                    ]
                },
                "capabilities": {
                    "filter": true,
                    "sort": true
                }
            }
            // ...
        }
    }
}

ATLAS uses this summary to drive the Session Browser filters, so that queries can run server-side.

In addition to constraints, the metamodel can include formatting rules for display and indicate whether the server supports filtering or sorting for a property.

Capabilities#

The session model already defines some properties — such as "state", "timestamp" and "type".

For each of these properties, the server can declare its capabilities:

{
    "state": {
        "filter": true,
        "sort": true
    },
    "timestamp": {
        "edit": true,
        "filter": true,
        "sort": true
    }
}

Constraints#

The metamodel can also describe the aggregate values a property has, or can take:

{
    "type": {
        "capabilities": {
            "filter": true,
            "sort": true
        },
        "constraints": {
            "values": [
                "Stream",
                "Model"
            ],
            "minLength": 1,
            "maxLength": 32
        }
    }
}

In this example, the type property:

  • is valid for sorting
  • is valid for filtering, and the client can offer "Stream" and "Model" as pre-set values
  • is valid for editing, but must take a value of 1-32 characters in length

Info

ATLAS uses "values" but currently does not use the other constraints.

Greater support will be added in future releases.

Display#

Pre-defined properties have an established description and display convention.

However, the server can define arbitrary properties within "details" and "extDetails", and describe them in the metamodel:

{
    "details": {
        "size": {
            "label": "Size",
            "description": "Size of the vehicle",
            "type": "string",
            "capabilities": {
                "filter": true,
                "sort": true
            },
            "constraints": {
                "values": [
                    "small",
                    "medium",
                    "large"
                ],
                "onlyValues": true
            }
        },
        "weight": {
            "label": "Weight",
            "description": "Just how heavy is this thing?",
            "type": "number",
            "capabilities": {
                "filter": true,
                "sort": true
            },
            "display": {
                "unit": "kg",
                "format": "%.2f"
            },
            "constraints": {
                "minimumExclusive": 0.0
            }
        }
    }
}

Info

ATLAS currently does not use the display rules, but may do so in future releases.

Warning

The Session Service does not currently provide a way to describe display rules.

Discovery#

details and in particular extDetails can represent very large meta-models — such as a detailed hardware and software setup parameters.

The service may choose not to expose some properties to the client by default, but still make them available for discovery.
Querying the metamodel produces results like this:

curl -H "Accept: application/json" "http://localhost:2650/rta/v2/session-metamodel/properties?query=details."

[
    {
        "id": "details.appearance",
        "label": "Appearance"
    },
    {
        "id": "details.taste",
        "label": "Taste"
    },
    {
        "id": "details.size",
        "label": "Size",
        "description": "Size of the vehicle"
    },
    {
        "id": "details.weight",
        "label": "weight",
        "description": "Just how heavy is this thing?"
    }
]

  1. "model of the model" ↩