[Zope3-dev] Proposed widget/schema work for the Rivah sprint (Thursday and Friday this week)

[Gary Poster]

On Aug 30, 2005, at 11:31 AM, Jim Fulton wrote:

> Gary Poster wrote:
>> On Aug 29, 2005, at 4:50 PM, Jim Fulton wrote:
>>> Gary Poster wrote:
>>> ...
>>>> 4 Recognize and document that the 'default' field argument is    
>>>> actually 'initial value'.
...
>>>
>>> I'm uncomfortable with this.
...
>> Initial value is a concept in XMLSchema (http://www.w3.org/TR/  
>> xmlschema-1/#key-iv).  The qoute is in W3C-speak, but I'm pretty  
>> sure  they are talking about what we are talking about.  I think  
>> it does  belong in a statement about a logical schema.
>
> I can't figure what they are saying. I mean i really have no clue.
> I asked my pointy-bracket consultant, but he couldn't make sense of
> it either, although he didn't think it had anything to do with that
> we were using the term for. :)

Heh, ok.

> Here's what we say about default in the schema package's README.txt:
>
>   "Default field values are assigned to objects when they are
>    first created."
>
> This is a statement either:
>
> - about the past history of an object, or
>
> - about some tool used to create an object.
>
> I don't really see that this is of value in a schema.  A schema
> constrains object values, bit default isn't about object values,
> it's about something that happened in the past.  There's no way to
> evaluate, for example, whether an object satisfies this aspect of
> it's schema.
>
> Furthermore, we rarely, if ever, use a default definition in a
> schema to constrain how an object is created. For example, I doubt
> this often effects how __init__ methods are defined. Rather, we use
> it to initialize forms.  We then create the object with whatever data
> we get from an add form.  IOW, we don't really use it is an initial
> value to create the object.
>
> I suggest that the default should become a field in a formlib form- 
> field
> definition, and should be deprecated from schema field.

Hm.  I'm not the one to quote computer science definitions, but I  
don't think the concept of schema is constrained to 'constraints'.  A  
schema is a data model.  The initial value of a given instance of the  
model, whether it be used for object creation or any other kind of  
model instantiation (e.g., collecting the data for a search form) is  
not unreasonably part of a data model.  I agree it is not a  
constraint, but I'm not sure that's pertinent.

That said, as we discussed verbally yesterday, a "purity" perspective  
suggests we are moving towards a more explicit three-layer cake for  
schema fields: interface, relationship, and form field.  If that  
perspective wins out, then yes, I agree that it fits better on the  
form field.

Gary