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