describedby or $schema attributes

[Jean-Hugues]

Hi,

Is instance1 or instance2 the correct way to specify the schema that
an instance must validate ?

var schema = {

"id" : "http://example.com/schema-test",
"extends" : { "$ref" : "http://json-schema.org/draft-03/schema#" },

"type" : "object",
"properties" : {
"test" : {
"type" : "string",
}
}
}

var instance1 = {
'$schema' : 'http://example.com/schema-test',
'test' : 'value'
}

var instance2 = {
'links' : {"rel" : "describedby", "href": 'http://example.com/schema-
test'},
'test' : 'value'
}


regards.

[Gary Court]

Neither. The "$schema" and "links" attributes are only used on JSON
schemas, not instances.

--Gary

[Gary Court]

Sorry, I didn't read your example closely enough. Because you are
extending the draft-03 schema in the "schema" variable, then
"instance1" specifies that "schema-test" is "instance1"'s schema;
which makes "instance1" a schema itself.

--Gary

[d2]

So, how to indicate the schema describing an instance in the
instance ? "instance2" is the correct way to do that ?

David

On 12 oct, 06:22, Gary Court <gary.co...@gmail.com> wrote:
> Sorry, I didn't read your example closely enough. Because you are
> extending the draft-03 schema in the "schema" variable, then
> "instance1" specifies that "schema-test" is "instance1"'s schema;
> which makes "instance1" a schema itself.
>
> --Gary
>
>
>
>
>
>
>
> On Tue, Oct 11, 2011 at 10:12 PM, Gary Court <gary.co...@gmail.com> wrote:
> > Neither. The "$schema" and "links" attributes are only used on JSON
> > schemas, not instances.
>
> > --Gary
>

[Gary Court]

I think this is what you are asking for:

instance.json:

{
"$schema" : "schema.json"
}

schema.json:

{
"links" : [
{
"rel" : "describedby",
"href" : "{$schema}"
}
]
}

--Gary

[Dean Landolt]

On Thu, Oct 20, 2011 at 3:48 PM, Gary Court <gary....@gmail.com> wrote:

I think this is what you are asking for:

instance.json:

{
       "$schema" : "schema.json"
}

schema.json:

{
       "links" : [
               {
                       "rel" : "describedby",
                       "href" : "{$schema}"
               }
       ]
}

This is a circular definition though. You've got a chicken/egg problem that can only really be solved at the application level by convention.

[Gary Court]

Yes, that is correct. JSON values have no meaning until a schema is
applied to it. So when you apply this schema against the instance, you
then understand that "$schema" is a reference to the schema that
should be validating the instance. Except a parser/interpreter already
knows this, so it's just there for semantics.

--Gary

[Dean Landolt]

I thought a parser/interpreter had to be told somehow that an instance is a schema for $schema (and $ref) to be meaningful? Is that not the case?

[Gary Court]

The meaning of any property (like "$schema" and "$ref") are based from
the schema that gives those properties meaning.

--Gary

[Dean Landolt]

Sure, but an instance doesn't yet have a schema when it's using $schema to say what it's schema should be, right? This is the chicken and egg problem.

[Nate Morse]

JSON is not like XML. JSON does not have a defined way of declaring a schema that it (should) adhere to, and JSON-schema does not require any additional conventions be added to an instance, so you can put anything you want in your JSON-instance, but there is no standard way of declaring a schema in your instance.  True?

 

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[Dean Landolt]

On Sat, Oct 22, 2011 at 12:11 PM, Nate Morse <morse...@gmail.com> wrote:

JSON is not like XML. JSON does not have a defined way of declaring a schema that it (should) adhere to, and JSON-schema does not require any additional conventions be added to an instance, so you can put anything you want in your JSON-instance, but there is no standard way of declaring a schema in your instance.  True?

That's definitely true of JSON itself, but JSON + JSONSchema is a slightly different beast -- it's feasible that in the context of a JSONSchema validation the validator should always treat the $schema property as a reference to a schema unless it's already aware of an instance and that instance overrides the meaning of $schema. I don't think this is the case, but it's one possible approach that could be spec'd. I'm not convinced that introducing the notion of a default schema would be a good idea, but it definitely has it's use cases.

[Dean Landolt]

Err, that is: unless it's already aware of a schema for an instance and that schema overrides the meaning of $schema.

[Nate Morse]

thanks,  now I see the "different beast" square in the eye. 

--