Re: SPEC : isA

steve ([email protected])
Thu, 15 Jun 1995 09:06:17 GMT0BST


> 1) Is there any requirement for the isA field to occur before other fields
> (except perhaps for the 'fields' field)? It make
> there is such a requirement, as you don't need to store the values of all
> fields as you parse an extension node. I have a feeling, looking at the
> sample node
> might be a good idea to make it explicit in the 1.1 spec.

my question of some time ago (which got no reply) was along a similar
line ; by introducing the isA field, the new node inherits the fields
from (multiple) parents. Therefore, should these be declared
(again) in the fields definition within the new node? I say they
should not - the whole point is that by declaring the node is based
on some standard type, any parser/run-time not capable of
understanding the new type can take some gui> as how to interpret
the node otherwise. For example

blueGlass {
isA "Material"
fields [ MFFloat refractiveIndex ]

diffuse 0 0 1
refractiveIndex 1.1
}

could be rendered opaque if a renderer cannot support refraction -
the Material fields are implied from the "isA" statement.

As an aside, I have implemented this in my VRML parser

Any comments?

> 3) The MFString type, while being a logical extension to the SF/MF
> convention, needs to be defined explicitly.

The name says it all. M=multiple, therefore MFString = multiple
strings, seperated by comma's and enclosed in [ ] as with all other
MFtypes

Hope that helps

Steve

=========================
Steve Ghee ( [email protected] )
Director of Technology

Division Ltd
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