Re: "YAML Easy Schemas"

Trans,

Thank you for putting the work into developing a schema language for YAML.

I do have one quibble. Where exactly is the spec for YPath? Most
people would be interested in finding all nodes with a given tag
property, and validating for that - but I can't even find how to do
that in the language.

I want to try and see if I understand your spec by trying it against
the "Invoice" example in the YAML spec:

http://www.yaml.org/spec/1.2/spec.html#id2761803

There are a few comments, which indicate possible directions for the
schema. All mistakes are mine. Example goes:

---
/[YPath expression for all nodes of tag <tag:clarkevans.com,2002:invoice>]:
  invoice: &mandatoryint
     type: int
     required: true #Shouldn't we use booleans like true and false?
  date:
     type: datetime #Indicate somehow that dates are required, but
times are not?
     required: true
  bill-to: &billing-schema-alias
     type: map
     required: true
     value: # We could refer to this by Ypaths, but it feels more
natural to embed in it the parent structure schema
       given: &amms # Short for "All Mandatory Strings Schema"
         type: str
         required: true
       family: *amms
       address:
           type: map
           required: true
           value:
               lines: *amms
               city: *amms # Or suburb.
               state: &aoss # Short for "All Optional Strings Schema"
                   type: string
                   required: false # Not every country has states or provinces.
               country: &aoss # Unnecessary if posting in the same country.
               postal: &aoss # Some countries don't use postcodes.
  ship-to: *billing-schema-alias # Yay for anchors and aliases!
  tax: &currency # Should indicate two decimal places - no more, no less.
    type: float
    required: true
  total: *currency
  comments: *amms
  product:
      type: seqorsing: # See below
      required: true
      value:
        sku: *amms
        quantity: *mandatoryint
        description: *amms
        price: *currency
...

I've probably made some indentation mistakes in typing in YAML, but
you get the gist. I think it is more natural to add a value property
to indicate the type of a mapping value, rather than use Ypath
expressions to refer to them. I also like the use of anchors and
aliases to save me typing in the same thing.

One more thing. In the original invoice example, "product" is a
sequence of separate products (in this case, 2). But if there is only
one product, is it necessary to express it as a sequence of one
product? Wouldn't it be more natural to let the user express it as a
single value in that case? I thought adding a type "seqorsing"
(sequence or singleton) would allow schema designers to validate
documents like this, while saving YAML writers a little bit of work.

What are your thoughts, Trans?

Best regards,
Peter


-- 
Email: [email protected]
WWW: http://www.pkmurphy.com.au/

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