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

XP> RE: Specifying the Persistence of Appmuxed Reference Objects

From: BIGELOW,JIM (HP-Boise,ex1) (jim.bigelow@hp.com)
Date: Fri Jan 24 2003 - 19:13:58 EST

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

    Hello,

    Dave Wissenbach wrote on 1/8/03
    > 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, ...
    >
    > If a given image is repeatedly used in the document, is the
    > image to be included repeatedly ...
    > ...
    > ... I am suggesting that persistence be
    > explicitly specified by the sending application by adding an
    > extended Content-Disposition header.

    The January 20th meeting of the PWG XHTML-Print working group discussed this
    proposal. Adding a reference count to the image header would indeed seem to
    tell the consumer of the multiplexed document when it can free the resources
    allocated for the image. However, it didn't seem to the participants that a
    producer of the document would always know how many references would be made
    and still be able to locate the image next to the 1st chunk that referenced
    the image.

    Alternatives were discussed in the meeting. The alternative were having the
    producer of the multiplexed document insert a chunk that would indicated
    when the document would not need an image any more, or having the producer
    insert some XHTML-Print element that would indicate when the consumer could
    release the resources for an image. In the first case, using a chunk header
    to indicate when the consumer could free an image won't work since the
    relative location of a chunk header can not reliably be associated with a
    processing point within the document. In the second case, adding new
    elements or processing instructions for the purpose of indicating when an
    image's resources could be freed was not deemed to be a viable alternative
    at this time.

    The group decided to reaffirm that a consumer could release the resources
    associated with an image after the document's reference to the image was
    processed.

    I propose that the following paragraph be added to the Section B.2 of the
    XHTML-Print spec:

    Producers and consumers of Application/Vnd.pwg-multiplexed entities, as
    defined in [MIMEMPX], should consider each image as having one and only one
    reference. The producer should not make assumptions about the buffering
    abilities of the consumer of an Application/Vnd.pwg-multiplexed entity and
    include a copy of an image for each reference to it. Consumers may release
    the resources associated with an image when the reference to it is
    satisfied, and are free to optimize references to identical images in an
    implementation dependent manner.

    Jim Bigelow,
    Editor: XHTML-Print & CSS Print Profile
    IEEE-ISTO, Printer Working Group
    http://www.pwg.org/xhtml-print
    Hewlett-Packard
    208-396-2068
    jim.bigelow@hp.com



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