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    SubjectRe: abstract file (multi-part one file or multiple files?)
    This is to some extent a disagreement over terminology. When we say
    "file", are we talking about the user interface or the implementation?
    At user level, a graphic, for example, it's attached thumbnail, and an
    attached description are part of the same complex "file", and it is a
    file, not a directory, even if the different parts are implemented as
    discrete unix type files, each with it's own name in a directory entry,
    on backing store. The directory-like implementation of it is
    meaningless to a user of the object.

    A multi-part "file" is a multi-part "storage object". What links
    the parts together is a filesystem storage object model that extends
    the "parent namespace linking associated non-directory leaf objects and
    subdirectories" semantics of unix directories to an implementation
    of storage objects that do not necessarily have the full directory
    semantics of explicit directories (like document files with nested
    streams: attempting to nest an explicit subdirectory like
    "/usr/local/this_or_that/" in one should return ENOTDIR, but nesting
    a multi-part storage object for a graphic image in one is reasonable).

    The complex document file is not a directory in the way that users
    understand directories, as an hierarchy of folders for storing objects
    that can be single-part or multi-part, but it needs to be implemented like
    a directory. The VFS must recognize that a multi-part storage object that
    is not explicitly a directory at user level has a directory implementation
    but has constraints on what can be nested in it that an explicit directory
    does not have.

    If you add per-file access control lists to unix filesystems, multi-part
    is a natural VFS view of unix files, too.


    Clayton Weaver

    "Everybody's ignorant, just in different subjects." Will Rogers

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