Semantic Model Mail Archive: SM> Re: IPP> 2 more signific

Semantic Model Mail Archive: SM> Re: IPP> 2 more signific

SM> Re: IPP> 2 more significant proposed increases in conformance requirements for the IPP Document object spec

From: Dennis Carney (dcarney@us.ibm.com)
Date: Mon Apr 21 2003 - 18:52:41 EDT

  • Next message: Dennis Carney: "Re: SM> 1 more significant proposed conformance change to the IPP Documen t object spec"

    I think that these ideas are good ones. However, I wonder why we didn't do
    anything about this before. In fact, in 2911, it is specifically called
    out that we purposely didn't handle this situation (2911, section 3.2.6.1:
    "There is no mechanism to allow for the next 'M' jobs after the first 'N'
    jobs."). Does anyone remember whether there was a good reason this issue
    was sidestepped?

    I've made 3 specific comments inline below, marked with <dmc></dmc>.

    Dennis Carney
    IBM Printing Systems

                                                                                                                                                       
                          "Hastings, Tom N"
                          <hastings@cp10.es To: sm@pwg.org
                          .xerox.com> cc: ps@pwg.org, ipp@pwg.org
                          Sent by: Subject: IPP> 2 more significant proposed increases in conformance requirements for the IPP
                          owner-ipp@pwg.org Document object spec
                                                                                                                                                       
                                                                                                                                                       
                          04/18/03 05:15 PM
                                                                                                                                                       
                                                                                                                                                       

    In summarizing the significant conformance requirement increases that we
    agreed to today in the review of the IPP Document Object spec review, I
    forgot two more:

    1. Add a REQUIRED way to the Get-Documents operation for the client to get
    the Documents following the limit requested in a previous request.

    So add the "start-after-document-number" (integer (0:MAX)) Operation
    attribute.

    2. Add a REQUIRED way to the Get-Jobs operation for the client to get the
    Jobs following the limit requested in a previous request.

    So add the "start-after-job-id" (integer (0:MAX)) Operation attribute.

    Please send any comments on these additions by Friday, May 2, COB.

    Here are the complete proposed text for these attributes and the updated
    "limit" Operation attribute:

    1.1 Get-Jobs ([rfc2911] section 3.2.6)
    This REQUIRED Job operation returns requested attributes of either
    completed
    or not completed Jobs. The following (new) "start-after-job-id"
    (integer(0:MAX)) Operation attribute is defined which in combination with
    the "limit" operation attribute ([rfc2911] section 3.2.6) permits a client
    to request selected ranges of jobs:
                 1.1.1 "limit" (integer(1:MAX)):
                             The client OPTIONALLY supplies this Operation
    attribute.
    The Printer MUST support this Operation attribute. It is an integer value
    that determines the maximum number of Jobs that a client will receive from
    the Printer even if "which-jobs" or "my-jobs" constrain which jobs are
    returned. The limit is a "stateless limit" in that if the value supplied
    by
    the client is 'N', then only the first 'N' jobs are returned in the
    Get-Jobs
    Response. If the client does not supply the "limit" attribute, the Printer
    responds with all applicable Jobs. However, if the client also supplies
    the "start-after-job-id" Operation attribute (section 4.2.2) with a value
    'M', the Printer returns the N Jobs starting with the Job following the one
    with "job-id" = 'M'.

    <dmc>
    We need to say what happens if job-id M is no longer in the list. I think
    the answer could be different for the two cases (non-completed vs.
    completed), making this a bit more complicated.

    If asking for *non-completed* jobs after job-id M, it is possible that M
    has completed since the client made the last call and is therefore no
    longer in the non-completed list. Unfortunately, this gets messy:
    1) If M completed successfully, the printer should return the first N
    non-completed jobs (i.e. the same as if M hadn't been specified at all).
    2) If M was canceled/aborted, it seems like the printer should ideally
    return the next job after M, *if* M hadn't been canceled/aborted. This
    extra attempt at correctness is, I guess, not really necessary, since the
    text below states that the caller can get strange results.

    Otherwise, if asking for *completed* jobs after job-id M, it is possible
    that M has been managed out of the completed list since the client made the
    last call. In *this* case, since completed jobs are returned in the
    opposite order of non-completed jobs, the printer should return an empty
    list. That is, since completed jobs are returned from newest to oldest, if
    M was managed out, jobs "after" (but actually printed before!) M are
    presumably also managed out, so there are actually no jobs "after" M in the
    completed list. This is the "correctly functioning" case of job-id M not
    being in the list, but there is also the "error" case where job-id M is
    just a bad value--it does seem strange to mandate that the printer return
    an empty list and success whenever the caller sends a bad
    "start-after-job-id" value.

    Maybe we want some new status-code: something like
    client-error-bad-start-id. Or we could possibly reuse client-error-gone or
    client-error-not-possible or some other existing status-code. Then there
    is just one answer for all the above cases: if M is not in the list, return
    an error and let the client decide what to do.
    </dmc>
                 1.1.2 "start-after-job-id" (integer(0:MAX)):
                             The client OPTIONALLY supplies this Operation
    attribute.
    The Printer MUST support this Operation attribute. If the client supplies
    this attribute with a job-id value 'M', the Printer MUST return Jobs
    starting with the Job that is after the one with "job-id" = 'M'. If the
    client does not supply this attribute, the Printer assumes a '0' value
    which
    causes the Printer to return any Jobs with any "job-id" that meet the
    requested criteria (specified by "which-jobs" and/or "my-jobs", etc.).
    When
    the client steps through the jobs N at a time, the client MUST set the
    "start-after-job-id" attribute from the "job-id' of the last Job returned
    in
    a previous Get-Jobs response (rather than just adding 'N', since Printers
    MAY assign job-ids out or order).
                             The client can detect when there are no more jobs
    when the
    Printer returns fewer jobs than requested by the "limit" Operation
    attribute
    ('N'). In the case when the last number of jobs returned is exactly N
    jobs,
    the client will make an extra request and receive no jobs back (still with
    a
    'successful-ok' success code). However, this case still meets the criteria
    for no more Jobs since the number of Jobs returned (0) is less than
    "limit"..
                             Note when the client steps through the Jobs
    supplying the
    "limit" and "start-after-job-id" Operation attributes in successive
    Get-Jobs
    requests, there are some race conditions which the client implementer needs
    to take into account:
                                         * For 'non-completed' Jobs
    (see [rfc2911]
    section 3.2.6.2), the Printer MUST return the Jobs in the order of the
    "expected time to complete" with the first expected to complete being
    returned first, etc. Because some Printers MAY: (1) process jobs out of
    order received, and/or (2) assign "job-id" in a non-monotonically
    increasing
    manner, occasionally a race condition MAY cause some jobs not be returned
    and some jobs MAY be returned more than once. The only way for a client to
    eliminate this race condition for 'not-completed' Jobs is to request all
    Jobs by supplying neither the "limit" nor the "start-after-job-id"
    Operation
    attribute.
                                         * For 'completed' jobs (see
    [rfc2911] section
    3.2.6.2), the Printer MUST return the jobs in the order of "newest to
    oldest" to complete. Therefore, no jobs will be missed and/or doubly
    returned.
    1.2 Get-Documents Operation
    This REQUIRED Job operation allows a client to retrieve the list of
    Document
    objects belonging to the target Job object. The client MAY also supply a
    list of Document attribute names and/or attribute group names. A group of
    Document object attributes will be returned for each Document object in the
    Job.
    This operation is similar to the Get-Document-Attributes operation (see
    section 3.5), except that this Get-Documents operation returns attributes
    from all Document objects contained in the Job object, instead of from a
    single selected Document object in the Job object. As with the
    Get-Document-Attributes operation the Printer MUST only return attributes
    that were submitted by a client when the Document object was created by the
    Create-Document, Send-Document, or Send-URI operations and possibly
    modified
    by the Set-Document-Attributes operation (see section 3.7).
    1.2.1 Get-Documents Request
    The client submits the Get-Documents request to a Printer. The
    Get-Documents is similar to the Get-Jobs operations (see [rfc2911] section
    3.2.6) except that there are no equivalents to the "which-jobs" and
    "my-jobs" Operation attributes.
    The following groups of attributes are part of the Get-Documents Request:
    Group 1: Operation Attributes
                 Natural Language and Character Set:
                             The "attributes-charset" and
    "attributes-natural-language"
    attributes as described in [rfc2911] section 3.1.4.1.
                 Target:
                             Either (1) the "printer-uri" (uri) plus "job-id"
    (integer(1:MAX)) or (2) the "job-uri" (uri) Operation attribute(s) which
    define the target Job object for this operation as described in [rfc2911]
    section 3.1.5.
                 Requesting User Name:
                             The "requesting-user-name" (name(MAX)) attribute
    SHOULD be
    supplied by the client as described in [rfc2911] section 8.3.
                 1.2.1.1 "limit" (integer(1:MAX)):
                             The client OPTIONALLY supplies this Operation
    attribute.
    The Printer MUST support this Operation attribute. It is an integer value
    that determines the maximum number of Documents that a client will receive
    from the Printer. If the client supplies the "limit" attribute with a
    value
    'N' and the "start-after-document-number" attribute with a value 'M', the
    Printer returns the N Documents starting with the Document after the one
    with "document-number" = 'M'. The limit is a "stateless limit" in that if
    the value supplied by the client is 'N', then only the first 'N' Documents
    are returned in the Get-Documents Response. If the client does not supply
    the "limit" attribute, the Printer responds with all Documents in the Job.
    However, if the client also supplies the "start-after-document-number"
    Operation attribute (section 4.3.1.2) with a value 'M', the Printer returns
    the N Documents starting with the Document following the one with
    "document-number" = 'M'.
    <dmc>
    Editorial: The above paragraph would flow better without the fourth
    sentence (the one starting "If the client supplies...").
    </dmc>
                 1.2.1.2 "start-after-document-number"
    (integer(0:MAX)):
                             The client OPTIONALLY supplies this Operation
    attribute.
    The Printer MUST support this Operation attribute. If the client supplies
    this attribute with a document-number value 'M', the Printer MUST return
    Documents starting with the Document that is after the one with
    "document-number" = 'M'. If the client does not supply this attribute, the
    Printer assumes a '0' value which causes the Printer to return Documents
    starting with "document-number" = '1' (which is the first document in the
    Job).
                             Note: canceled Documents (see section 3.7) are
    still
    returned, but deleted Documents (see section 3.8) are skipped over, since
    they don't exist (leaving gaps in the "document-number" sequence).
    <dmc>
    Due to the fact that deleted Documents disappear, we have the same problem
    as discussed above: Document number M might no longer exist. The expected
    behavior for this should be similar to that decided upon for jobs, I would
    think; however, for Document objects, the "ideal" behavior would be to
    return the Documents starting with the first after Document M that hasn't
    been deleted. Unfortunately, this "pretend like M is still there" strategy
    doesn't really work as a general solution in the Get-Jobs case.
    </dmc>

    Please send any comments on these additions by Friday, May 2, COB.

    Thanks,
    Tom



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