RE: proposed new Media Type application/iges

Steve Waterbury (
Thu, 16 Mar 1995 09:57:10 -0500

Curtis Parks of NIST wrote:

> > Media type name: application
> > Media subtype name: iges
> > IGES is a commonly used format for CAD model (3-D or 2-D) interchange.

... to which Jan Hardenbergh responded:

> An alternative is to make it part of a new content (Media?) type, as
> opposed to a subtype of "application". IGES serves many applications.
> We are working toward proposing "world" as part of the VRML effort.

... to which Keith Moore adds:

> The top level in MIME types is designed to allow filtering by gateways
> between different kinds of messaging systems (so that you don't try to
> ship audio/* to a pager or image/* to voice mail), and also to provide
> default user agent handling of content-types. So the argument needs
> to be pitched in these terms.

Curtis and I and some others had some discussion of which
existing MIME type, if any, was the most appropriate for IGES.
We ended up without a strong opinion, but were thinking
that "application" was about as generic as we could get.

> 1) do 3D models require different "hardware" support or support from
> the transmission medium to be usable, from (say) that for image/* or
> application/*?

Not sure what is meant here ... application/* and image/* don't
say much: the existing image subtypes are all raster formats,
but the Computer Graphics Metafile (CGM) has been proposed as a
subtype of the image/* type, and a CGM file has a lot more structure
than a raster file, so that confused us.

Actually, an uncompressed IGES file is just ASCII, so it is
simpler than many of the binary files in the application/*
or image/* types. I suggested that for transmission/
gateway purposes, IGES could be a text/* type :-) ... so I
don't think we really understand the intent of the top (type)
level in the MIME system -- the subtype is the easy part!

> 2) is there a default user agent behavior that applies to *all* 3D
> models in your proposed world/* class?

Jan will have to address that, as it is his proposal, but I
will offer the following on IGES:

One possible scenario for default user agent handling of
IGES content is based on the fact that IGES files incorporate
version and application-type (in IGES parlance, Application
Protocol or "AP") information within the file. So the scenario
would be to have the MIME-capable user agent pass the IGES
content to a "mediator" tool, which would read the version
and AP information from the content and could be set up with a
series of behaviors based on that information -- e.g., to pass the
content directly to the preferred viewer or CAD tool for that
version and set of AP's, or to present the version and AP
information to the user with a user-configured pick list of
appropriate viewers/tools to pass the content to.

I don't know whether this scenario is consistent with the concept
of the proposed world/* type. We would love to get some concrete
advice on this from the IANA or some knowledgable person!

oo _\o
\/\ \
____________________________________________ oo ____________
"Sometimes you're the windshield; sometimes you're the bug."
- Knopfler

Stephen C. Waterbury Assurance Technologies Division
Code 310, NASA/GSFC Staff Specialist
Greenbelt, MD 20771 Computer-Aided Engineering
Phone/FAX: 301-286-7557/1695
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