XP Mail Archive: Re: XP> Specifying the Persistence of Appmu

Re: XP> Specifying the Persistence of Appmuxed Reference Objects

From: ElliottBradshaw@oaktech.com
Date: Wed Jan 08 2003 - 16:43:45 EST

  • Next message: BIGELOW,JIM (HP-Boise,ex1): "RE: XP> Specifying the Persistence of Appmuxed Reference Objects"

    We've also played with idea of using the "declare" attribute on the obj
    element. The idea being that if you declare the object, that means you
    want to store its contents for the duration of the job.

    I don't know if this exactly matches what the W3C had in mind for this
    attribute. It would also be limited to the object element. But for images
    the object element is OK, and it has the advantage that it would work in
    any XHTML-Print configuration, regardless of transport.

    ------------------------------------------
    Elliott Bradshaw
    Director, Software Engineering
    Oak Technology Imaging Group
    781 638-7534

                                                                                                    
                        "WISSENBACH,DAV
                        ID To: "'xp@pwg.org'" <xp@pwg.org>
                        (HP-Boise,ex1)" cc: "BIGELOW,JIM (HP-Boise,ex1)"
                        <david_wissenba <jim.bigelow@hp.com>
                        ch@hp.com> Subject: XP> Specifying the Persistence of
                        Sent by: Appmuxed Reference Objects
                        owner-xp@pwg.or
                        g
                                                                                                    
                                                                                                    
                        01/08/2003
                        03:29 PM
                                                                                                    
                                                                                                    

    Dear people,

    I (Dave Wissenbach, an HP engineer) have a small nit to pick with the
    specification and usage of the application/multiplexed format which I
    explain below:

    The MIME Application/Vnd.pwg-multiplexed document format is provided to
    minimize memory requirements in a printer. This requirement to minimize
    memory usage suggests that referenced image data should be thrown away as
    soon as the images have been rendered. Yet I have found no documentation to
    suggest that this is indeed the case, other than the suggestion in the
    application/multiplexed RFC3391 that objects that are out of scope no
    longer
    need to be stored, and can then be discarded, and that a mechanism is (or
    should be?) provided for that purpose.

    If a given image is repeatedly used in the document, is the image to be
    included repeatedly, but with a different Content-ID each time? HP has a
    prototype MIME multiplexer that specifies Content-Location: instead of
    Content-ID in the header for each referenced object. I suppose that the
    advantage of this approach to a multiplexed document is that the root
    document need not be modified. But then we have the problem that the
    multiply referenced object needs to persist over the entire course of
    rendering the root XHTML-Print document.

    Even the multiplexing application always uses Content-ID, and alters the
    root XHTML-Print document to reference a different Content-ID each time, we
    have the problem of wastefully resending the document.

    To solve these problems, I am suggesting that persistence be explicitly
    specified by the sending application by adding an extended
    Content-Disposition header. See RFC 2183, Communicating Presentation
    Information in Internet Messages: The Content-Disposition Header Field for
    a
    method to extend the Content-Disposition header.

    If an object is to persist, I suggest the following in the Message Header
    for that object:

    CHK 2 570 MORE
    Content-Type: image/jpeg
    Content-Location: Rachel.jpg
    Content-Disposition: inline;
      persistence=refcount;
      references=5;

    Image Data here...

    Or for a watermark that must appear on every page

    CHK 2 570 MORE
    Content-Type: image/jpeg
    Content-Location: Watermark.jpg
    Content-ID: Content-ID: <49568.45876Watermark.jpg@hp.com>
    Content-Disposition: inline;
      persistence=infinite;

    Values for persistence would be once, refcount or infinite

    Value for reference count would be 1 and above.

    If the Content-Disposition header field is missing, the XHTML-Print
    interpreter would free the image as it was consumed with the first
    rendering.

    As an alternative to this proposal we should document the understanding
    that
    Content-ID always be specified, and that each reference, even to the same
    image, be required to represent the data inline.

    There is probably one other way to make a persistent image, which is to
    assign an objectID in the header of the html document, but I prefer to have
    a solution that lets a web-based document be examined and mime-wrapped
    without further modification.

    Dave



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