Re: [Json] Another problematic JSON Schema use-case

[Austin William Wright <[e-mail]>]

On Thu, May 26, 2016 at 8:56 AM, Tim Bray <[e-mail]> wrote:

> So, to close the loop, here's how I worked around the problem. I
> auto-processed my large schema with a Ruby script to generate a small
> schema for each of the "Type":"Animal/Vegetable/Mineral" variations, then
> if the large schema reports any errors, I run through the objects
> validating each with the appropriate micro-schema.  This way, I almost
> always get a human-comprehensible error message.
>
> Not optimal, but better than writing a fully procedural validator by hand.
>
I now recall my earlier solution, which is similar enough to this: If two
objects carry different data, they should be described by different schemas.

Things of type "Plant" should validate against a Plant schema, which
includes (with allOf) a reference to the generic schema.

So instead of the schema I listed in my first post to the thread, you would
use a schema like:

{
    "id": "http://example.com/Plant",
    "allOf": [{"$ref":"http://example.com/Thing"}],
    "properties": {
        "Type": {"enum":["Plant]}
    },
    "required": ["Thing", "Genus", "Species"]
}

This would also go over the wire with the profile="http://example.com/Plant"
media type parameter.

Notice how the allOf acts like the "subclasses" operator in a dynamic
language (like PHP or maybe Ruby; as opposed to C++ which is static or
maybe ECMAScript which is prototypical): A Plant is also a Thing, but a
Thing doesn't necessarily have the data fields found in Plant.

Please let us know if you've considered something like this, and how such a
solution would work for you.

Digging a little more advanced into JSON Schema, there's no reason an
instance can't actually be describedby multiple schemas. A server could say
"Accept: application/json;profile=Thing" and the client could send back
"Content-Type: application/json;profile=Thing;profile=Plant". Or maybe just
"Content-Type: application/json;profile=Plant" if the server understands
the JSON Schema semantics. I'll have to do some digging and see if this
would be legal...

Thanks,

Austin.