Comments on DQL from Joe Rockmore

From: Richard Fikes (
Date: 09/19/02

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    FYI --
    -------- Original Message --------
    Subject: DQL
       Date: Thu, 19 Sep 2002 08:06:40 -0700
       From: joe rockmore <>
         To: fikes@KSL.Stanford.EDU
    richard...i read your recently-released DQL abstract specification with
    interest.  a few comments that may improve it (i don't have any
    substantive comments on the language design, as this is not my
       * i think examples throughout would help the explanations.
       * i think you need to better introduce your idea of what an answer KB
         is.  you state "The set of DAML sentences that are used by the
         server in answering a query is referred to as the answer KB." which
         is clear enough, but  i think most people would not think of this
         as a knowlege base (although they might think of it as a base of
         knowledge from which the answers derive).  in particular, many
         people will think of a set of DAML sentences as defining the
         ontology, since that is the strong focus of OWL.  i think what you
         really mean is that an answer KB is the set of all sentences about
         instances (what OWL calls individuals), where they are interpreted
         according to the ontology (which is comprised of sentences about
         classes, properties, etc.).  is this correct?  if so, i think a bit
         more explanation (and some examples) would help clarify this point.
       * i am still bothered by your approach to answer bundles with
         continuation (cf our discussions at the last PI meeting).  you
         address some of my concerns in the paragraph titles '"How Many"
         Queries' (although i had a hard time parsing that title, thinking
         you meant how many queries, rather than queries about how many
         answers).  it seems to me that a server, if it can process a set of
         continuations and eventually reach termination, can do so and
         return the number of answers that it will provide if the queryer
         keeps asking for contiuations.  that is, not all servers will reach
         termination, but if they do, then they can do so and return the
         number of answers before providing any actual answers.  i think you
         need to somehow include this type of answer, as if it takes, for
         example, 100,000 continuations until termination, i might want to
         know that before i keep asking for more answers.  i do understand
         the thorniness of this issue, but i think you can under some
         circumstances (but not all) provide an answer to "how many"
         queries, and DQL should support this.
       * i understand that you are not ready for specifying the response to
         a justifcation request, but can you tell me what your thinking is
         along these lines?  i would like to see something here like a
         backtrace of any inferences made to provide an answer (assuming its
         not explicitly stated in some DAML sentences about the instance),
         but other than that i am not sure what should, or could, be
         included.  please enlighten me.
       * in the discussion on answer bundles, you state, "There is no
         provision in DQL for a query to indicate an upper bound on the
         total number of answers in a dialog, but a client can terminate a
         question-answering dialog at any time by ... simply by not
         requesting any further continuations."  doesn't this approach
         require the server to maintain the state of the continuation,
         perhaps forever, in the case that the client later asks for
         continuation?  or is there some kind of timeout (that you said you
         are not addressing) here that says after some time period the
         server can safely drop the state of a query, and the dialog would
         have to start from scratch if the client wanted more answers?
     thx for helping me understand this important aspect of DAML.  i expect
    that Horus will migrate to DQL as soon as practical, and it is important
    that we understand what is going on, as well as have confidence that it
    is stable in its basic form.
    a. joseph rockmore, phd       -|-        cyladian technology consulting
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