[comp.mail.multi-media] PostScript as MMmail

nsb@THUMPER.BELLCORE.COM (Nathaniel Borenstein) (08/15/90)

I hate to say anything nice about using PostScript as a multi-media mail
standard, but I think the main problem with PostScript portability, in
this context, is that the language can make reference to external
resources (such as library files) which don't necessarily follow the
program to another site.  This is a problem that almost any language
could have, and could be solved in two ways for multimedia mail:

1.  Disable all such features.  In particular, this means the language
can't have a library.

2.  Modify the transport layer so that it recognizes the resources
required by each message, and packages them up to send to the next site
if necessary.  Thus if mail requires the "foobar" library, the first MTA
will ask the second MTA if it has the foobar library (appropriate
version number, presumably) and, if not, will transmit it to the
receiving site.

The second approach is somewhat flawed because it's hard to be sure  two
versions of a library are identical.  However, it closely resembles what
mail transport will have to look like when costly media such as video
are sent through the mail anyway, in my belief.  (You don't want to put
the video in the body, because many steps of the transport may be within
a domain where the video is uniformly accessable using some kind of
token.)

At any rate, I doubt that PostScript is any less portable than any other
representation that permits external references.  It seems to be a
pretty well-defined language.  -- Nathaniel

tcrowley@DIAMOND.BBN.COM ("Terry Crowley") (08/15/90)

I've found PostScript to be very portable.  The problems I've seen have
been due to programs that generate incorrectly structured postscript
and then run it through a page-reversal process, which generates a bad
postscript file.  Older versions of the transcript spooling software from
Adobe would automatically run files through the page reversal process
(because the early LaserWriters made things come out backwards).  The
following quote comes from the Adobe file server message on getting and
printing PostScript documents from their file server:

     PRINTING: Some of you are running old versions of TranScript (Unix 
     spooling product) and have old LaserWriters.  If you have PAGE REVERSAL 
     turned on in older versions of TranScript (prior to version 2.0, I 
     think), you will have problems with these documents.  The symptom of 
     this problem is the following error message (or no printout whatsoever):

     	%%[Error: undefined; OffendingComment: BEGINPAGE]%%

     If you see this error OR if nothing prints and your pages normally come
     out of the printer with the last page first, then ADD ONE LINE to the
     beginning of the PostScript file before you print it.  This line should
     contain just the two %! characters, and a carriage return.  The first
     two lines of the file would then look like this:

     	%!
     	%!PS-Adobe-2.1

You (Dave Crocker) may have been running into this problem frequently,
making it appear that their were significant portability problems.

At to Nathaniel's message, most Postscript print drivers that I'm aware
of don't generate references to external libraries.

Terry Crowley