[x3d-public] Agenda for X3D WG Open Meeting Wednesday 10th May 2017

[Richard F. Puk]

Hi, Yves --

What I meant by "originally intended" was that it is consistent with other
data types. For example, an MFFloat expressed as [] represents an array with
no elements. Similarly, an MFString expressed as [] represents an array with
no elements (i.e., no strings). However, an MFString expressed as [""]
represents an array with on element consisting of an empty string. Since the
implementation of an MFString is often done by providing an array of
pointers to the strings in the array, an empty string would have a pointer
but no content. I believe that this is what is expressed in both VRML and
X3D. Since I participated in all of the discussions back when VRML and X3D
were each being designed, I know that consistency of field type was an
important factor.

  -- Dick

/******************************************
| Richard F. Puk, Ph.D., President
| Intelligraphics Incorporated
| 7644 Cortina Court
| Carlsbad, CA  92009-8206
| Tel: +1-760-753-9027  Mobile:  +1-760-809-9027
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-----Original Message-----
From: Yves Piguet [mailto:yves.piguet at gmail.com] 
Sent: Friday, May 12, 2017 7:53 AM
To: Richard F. Puk
Cc: Roy Walmsley; Don Brutzman; X3D Graphics public mailing list
Subject: Re: [x3d-public] Agenda for X3D WG Open Meeting Wednesday 10th May
2017

Dick, what do you mean with "originally intended"? Which standard, or which
informal proposal by which author?

My reaction was wrt Don Brutzman's suggestion to permit unquoted strings in
XML Encoding MFString fields to be accepted as a single-element MFString.
Then the empty XML attribute could be interpreted either as an MFString
containing a single empty string (following Don) or as an MFString with zero
element (following the current X3D XML Encoding standard).

You can add special cases to try and guess the intent of the author and
remove any residual ambiguity, but then you end up with something like HTML5
where each "syntax error" has a well-defined outcome thanks to an utterly
convoluted description of what a parser is supposed to do. I don't like
that, I strongly object to that for X3D. XML provides a rigid framework
which can still be easily edited by hand, not a loose format like HTML. But
it's only my opinion.

Yves


> On 11 May 2017, at 21:24, Richard F. Puk <puk at igraphics.com> wrote:
> 
> Hi, Roy --
> 
> I think that [""] represents an MFString construct containing one 
> element, an empty string. Then [] is an MFString construct that contains
no elements.
> I think that this is what was originally intended.
> 
>  -- Dick
> 
> /******************************************
> | Richard F. Puk, Ph.D., President
> | Intelligraphics Incorporated
> | 7644 Cortina Court
> | Carlsbad, CA  92009-8206
> | Tel: +1-760-753-9027  Mobile:  +1-760-809-9027
> | Email:  puk at igraphics.com
> \******************************************
> 
> 
> 
> -----Original Message-----
> From: x3d-public [mailto:x3d-public-bounces at web3d.org] On Behalf Of 
> Roy Walmsley
> Sent: Wednesday, May 10, 2017 3:58 PM
> To: 'Yves Piguet'; 'Don Brutzman'
> Cc: 'X3D Graphics public mailing list'
> Subject: Re: [x3d-public] Agenda for X3D WG Open Meeting Wednesday 
> 10th May
> 2017
> 
> Hi Yves,
> 
> An empty MFString array would have no values. Now that is an 
> interesting one we didn't discuss today!!!
> 
> According to the current standard it would be simply [''], i.e. two 
> single quotes or apostrophes. However, if we accept the changes 
> discussed today, one of which was that an MFString field with only one 
> value could dispense with the outer set of quotes and be encoded as an 
> SFString, then that could present a dilemma. It would mean that it 
> could be interpreted as a single value, which was the empty string, or 
> an empty MFString array. These are not the same things, and so this 
> case would require specific wording in the text, for clarity.
> 
> Thanks again, Yves,
> 
> Roy
> 
> -----Original Message-----
> From: x3d-public [mailto:x3d-public-bounces at web3d.org] On Behalf Of 
> Yves Piguet
> Sent: 10 May 2017 21:40
> To: Don Brutzman <brutzman at nps.edu>
> Cc: X3D Graphics public mailing list <x3d-public at web3d.org>
> Subject: Re: [x3d-public] Agenda for X3D WG Open Meeting Wednesday 
> 10th May
> 2017
> 
> Excuse me if I've missed it, but how do you specify an empty MFString
array?
> If double quotes are optional, '' (empty attribute value) would mean 
> an empty SFString, i.e. [""] if an MFString is expected, not [].
> 
> Yves
> 
> 
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