Browse Prior Art Database

IPDS Nack Recovery in an Enhanced Expert System Framework

IP.com Disclosure Number: IPCOM000106168D
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 6 page(s) / 212K

Publishing Venue

IBM

Related People

Mastie, SD: AUTHOR

Abstract

There are hundreds of IPDS Negative Acknowledgments (NACKs), most of which require different messages and complex recovery actions to occur. Not surprisingly, Error Manager code is therefore quite difficult and knowledge-intensive, and traditional Error Manager organizations specify complex in-line code after a NACK is recognized. A more recent improvement was to specify "table driven" error management, but this has inefficiency in representation and storage (each NACK can have many action codes, and each unique NACK/action-code pair needs to be represented), and does not easily allow for independent reasoning about the proper recovery actions and messages for an individual NACK.

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IPDS Nack Recovery in an Enhanced Expert System Framework

      There are hundreds of IPDS Negative Acknowledgments (NACKs),
most of which require different messages and complex recovery actions
to occur.  Not surprisingly, Error Manager code is therefore quite
difficult and knowledge-intensive, and traditional Error Manager
organizations specify complex in-line code after a NACK is
recognized.  A more recent improvement was to specify "table driven"
error management, but this has inefficiency in representation and
storage (each NACK can have many action codes, and each unique
NACK/action-code pair needs to be represented), and does not easily
allow for independent reasoning about the proper recovery actions and
messages for an individual NACK.  Basing IPDS error recovery on
action codes is a convenient short-cut for some printers, but since
not all IPDS printers have action codes, this requires additional
complexity to simulate action codes for some printers, and still
needs to take specific messages/actions for the individual NACKs
within the action code equivalence classes.

      NACKs are a dynamic part of IPDS, and it is a requirement of
any Error Manager to be able to easily add new NACKs, and change
recovery/messages for existing NACKs.

      Proper handling of NACKs is imperative to managing the two-way
IPDS communication between IPDS print driver software and intelligent
printers.  Proper handling of NACKs is a prerequisite to
system-managed recovery from print-time errors.

      A knowledge-Base representation of all IPDS NACKs is
implemented, complete with a complex inference engine, to do correct
NACK recognition and classification.  The process of recognition and
classification is Action-code independent, so it holds for all IPDS
printers, and is completely separated from the implementation of the
recovery actions from the NACK(s) being handled.  This invention
redefines the steps of IPDS NACK recovery to fit within a modified
Expert System framework.

      This invention is instantiated in the PSF/2 product.

      A summary of the algorithm steps which implement this invention
in PSF/2 follows:

*  For each NACK received from the printer, an Inference Engine calls
a Knowledge Base (henceforth "KB") to see if the NACK is recognized.

1.  If the NACK is recognized, a sequence of recovery actions and
    messages which would be appropriate for the NACK are specified
    and attached to the NACK.  In Expert Systems terminology this
    would be called a "recovery script"; in PSF/2, it is implemented
    as two ordered vectors, one each for actions and messages.

2.  If the NACK is not recognized by the Knowledge Base, the
    Inference Engine builds an appropriate recovery script for the
    unrecognized NACK.

3.  NACK actions and messages can be modified by the application of
    meta-knowledge by the Inference Engine.  This allows the
    application of special handlin...