Structures

Named data structures present complex JSON objects that can be referred to from either Properties, or Operations parameters, or even from other Structures.

Definition

The format for declaring a structure follows the JSON Schema:

{
    "structures": {
        "name1": { /* JSON-schema-1 */ },
        "name2": { /* JSON-schema-2 */ },
        "name3": { ... }
    }
}

A sample “structures” section looks as follows:

{
    "structures": {
        "Person": {
            "type": "object",
            "properties": {
                "firstName": { "type":"string", "required":true },
                "lastName": {"type":"string" },
                "books": {
                    "type": "array",
                    "items": {
                        "type": "string"
                    }
                }
            }
        }
    }
}

Once declared, it is possible to refer to such a structure by its name, for example:

{
    "id": "http://demoapp.apsdemo.org/some/type/1.0"
    "properties": {
        "owner": {
            /* Referencing the "Person" structure */
            "type": "Person"
        },
        "employee": {
            /* Referencing the "Person" structure */
            "type": "Person"
        },
    },
    ...
    "structures": {
        /* Actual data declaration */
        "Person": {
            "type": "object",
            "properties": {
                "firstName": { "type":"string", "required":true },
                "lastName": {"type":"string" }
            }
        }
    }
}

It is also possible to refer to such a structure from other APS types through its fully-qualified name:

<APS Type ID>#<Structure Name>

Examples:

http://demoapp.apsdemo.org/some/type/1.0#Person
http://aps-standard.org/types/mail/mailbox/1.0#Socket

To refer to the “Person” structure from another APS type use the following definition:

{
    "properties": {
        "person": {
            "type": "http://demoapp.apsdemo.org/some/type/1.0#Person"
        }
    }
}

Resource Counters

Let us look at one more practical example. Resource counters in APS applications are based on the Counter structure defined in the APS core type Resource as:

{
    "apsVersion": "2.0",
    "id": "http://aps-standard.org/types/core/resource/1.0",
    "name": "Resource",
    ...
    "structures": {
        "Counter": {
            "type": "object",
            "properties": {
                "usage": { "type": "integer" },
                "limit": { "type": "integer" }
            }
        },
        ...
    }
}

When adding resource counters to your application, use the following example of property definition:

{
    ...
    "properties": {
        ...
        "diskusage": {
            "type": "http://aps-standard.org/types/core/resource/1.0#Counter",
            "description": "Diskspace Usage",
            "unit": "gb"
        },
        "cpuusage": {
            "type": "http://aps-standard.org/types/core/resource/1.0#Counter",
            "description": "CPU usage - number of CPU cores",
            "unit": "unit"
        },
        "memoryusage": {
            "type": "http://aps-standard.org/types/core/resource/1.0#Counter",
            "description": "Memory usage",
            "unit": "mb"
        }
    }
}

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