Re: misconceptions about MIME [long]

Dan Connolly (connolly@pixel.convex.com)
Tue, 27 Oct 92 17:03:40 CST 

Message-Id: <9210272303.AA18485@pixel.convex.com>
To: Larry Masinter <masinter@parc.xerox.com>
Cc: NED@sigurd.innosoft.com, nsb@thumper.bellcore.com,
Subject: Re: misconceptions about MIME [long] 
In-Reply-To: Your message of "Tue, 27 Oct 92 14:38:18 PST."
             <92Oct27.143829pst.101795@poplar.parc.xerox.com> 
Date: Tue, 27 Oct 92 17:03:40 CST
From: Dan Connolly <connolly@pixel.convex.com>


>If I wish to retrieve the document, say to view it, I might want to
>choose the available representation that is most appropriate for my
>purpose. Imagine my dismay to retrieve a 50 megabyte postscript file
>from an anonymous FTP archive, only to discover that it is in the
>newly announced Postscript level 4 format, or to try to edit it only
>to discover that it is in the (upwardly compatible but not parsable by
>my client) version 44 of Rich Text. In each case, the appropriateness
>of alternate sources and representations of a document would depend on
>information that is currently only available in-band.

What methodology do you propose to prevent this situation? It looks
like a very hard problem indeed. But MIME makes a good stab at
standardizing practices that are going on now. I think we can prevent
further divergence in the CSCW and global hypermedia communities
by adopting MIME now.

In short: I think MIME will not completely solve the problem you
stated, but it _will_ do more good than harm.


>I believe that MIME was developed in the context of electronic mail,
>but that the usage patterns in space and time of archives, database
>services and the like require more careful attention (a) to
>out-of-band information about format versions, so that you might know,
>before you retrieve a representation, whether you have the capability
>of coping with it, and (b) some restriction on those formats which
>might otherwise be uncontrollable.

The function you describe in (a) above is commonly known as the
halting problem. No can do. Formats mentioned in (b) are called
turing machines: postscript programs, excel macros, etc. And life
gets only a little easier if you get rid of turing machines.

If I understand you correctly, every document must be annotated
with all of the resources it requires. For example:

* TIFF image. 400x760. 16 colors (pantone #416, #450, #23, ...)
zbar compression. 10k compressed. 160k uncompressed.

* postscript document. A4 page size. Peak virtual memory usage: 2.7mb
on a LaswerWriter IINT. Fonts: courier (4-18pt), times, New Century Schoolbook.

* xwd image. 24 bit direct color image. Requires patch #18 on
the RS/6000 X server.

I think MIME starts to look like a _very_ reasonable level of
standardization given the possible spectrum.

Dan