Re: [apps-discuss] JSON Schema considered harmful

Actually you can do a lot more than Wildcards in XML Schema.

And no, it is not a good idea to try. That is why SAML 2.0 became necessary
as people had told me to use model groups in SAML 1.0.

On Thu, Sep 20, 2012 at 12:26 PM, Erik Wilde <dret@berkeley.edu> wrote:

> hello all.
>
>
> On 2012-09-20 09:02 , Nico Williams wrote:
>
>> So, while I have no problem with specific complaints about
>> shortcomings of one or another schema language, I do object to the
>> idea that because they fail to denote semantics we should not use
>> them.
>>
>
> that's my general feeling as well. schemas are not able to and not
> designed to completely capture protocol semantics, but they provide a good
> starting point, and allow some level of formalism which then needs to be
> augmented with documentation.
>
>
>  Regarding specific complaints...  I am not very familiar with XML
>> Schema, so I can't say much about it and extensibility.  ASN.1 has
>> extensibility rules nowadays, and often uses of ASN.1 predating
>> extensibility rules are nonetheless extensibile (sometimes we need to
>> resort to negotiation of extensions, but that's OK).  I suspect that
>> the situation w.r.t. XML Schema extensibility is not as dire as you
>> paint it.
>>
>
> imho, the real challenge is to *design* a good extension model for a
> language; coding it in a schema language then is just an exercise in
> figuring out what can be done in that specific language. in XSD, all you
> can do is to use wildcards (possibly refined by namespace specifications
> for them), and then you have to add documentation saying how processors are
> supposed to handle wildcards (ignore, interpret, stop, ...). extension
> rules cannot be fully captured (such as saying that extensions are not
> allowed to change the semantics of any fields in the base format), but at
> least the schema describes the base syntax, and also validates instances
> containing extensions.
>
> i have to admit that i am really curious why the seasoned spec writers
> that have voiced general concerns about the usefulness of schema languages
> are feeling this way, but so far i have not really understood what they are
> saying. could somebody please try again, i'd really like to understand why
> the general idea of describing protocol syntax in a semi-formal (as opposed
> to non-formal) way is considered a bad idea.
>
> thanks a lot and kind regards,
>
> dret.
>
> --
> erik wilde | mailto:dret@berkeley.edu  -  tel:+1-510-2061079 |
>            | UC Berkeley  -  School of Information (ISchool) |
>            | http://dret.net/netdret http://twitter.com/dret |
>
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