Re: [cgmo-webcgm] WebCGM traversal routines

[Forrest Carpenter <forrest@sdicgm.com>]

All,

In our implementation the first child is one, because it is the first child 
in order
of the sequence of the cgm file. It makes no sense to make the last child 
the first
child because it is the foremost object in a group. This is backward from 
the way
most tree structures work. In multi-picture files would the first picture 
become the
last picture?

Forrest


At 10:37 AM 10/7/2004, you wrote:
>Hi all,
>
>   I have a question regarding the WebCGM DOM traversal routines.  I
>   have to admit, this one took me by surprise.  Let's take the
>   following WebCGM document snippet as an example:
>
>   BEGAPS 'group' ...
>   BEGAPSBODY;
>     BEGAPS 'one' ...
>     ...
>     ENDAPS;
>     BEGAPS 'two' ...
>     ...
>     ENDAPS;
>     BEGAPS 'three' ...
>     ...
>     ENDAPS;
>     BEGAPS 'four' ...
>     ...
>     ENDAPS;
>   ENDAPS;
>
>   In your opinion; what is the firstChild of 'group'?  Being accustomed
>   to the XML world, I was convinced that the answer would be 'one';
>   but the existing Isodraw code tells me otherwise, it claims that
>   'four' is the firstChild.  Dieter then explained that 'four'
>   is the firstChild since it's the foremost object of the group.
>   Ok, now it makes sense to me.
>
>   We believe (and please correct us if we are wrong) that other
>   private APIs from vendors of this group behave like ours; that a
>   firstChild of a group is not the first child based on file order but
>   instead, the foremost element (visual tree order).
>
>   So the question is; do we want to adopt the XML/SVG approach (file
>   order) or stick with current practices of CGM vendors (visual tree
>   order)?
>
>   Note: if we do stick with current practices, I would recommend
>   changing the names of these APIs or else they'll be confused with
>   XML/SVG APIs.
>
>   I don't know what my preference is on this.  I'm some times in
>   favour of the XML/SVG approach (since script writers are used to
>   this) but I could be convinced otherwise since WebCGM files are
>   binary (so your are left with what you see on screen).  What is
>   problematic for me are the XML metadata nodes:
>
>   BEGAPS 'group' ...
>   BEGAPSBODY;
>     BEGAPS 'foo:simpleData' ...
>     ...
>     ENDAPS;
>     BEGAPS 'foo:complexData' ...
>     ...
>     ENDAPS;
>   ENDAPS;
>
>   Why would the firstChild of 'group' be 'foo:complexData'?
>
>   Obviously looking for your input,
>
>   Regards,
>
>--
>  Benoit                 mailto:benoit@itedo.com