Re: New DQL Specification

From: patrick hayes (
Date: 06/10/02

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    >All this brings up the basic point:
    >     What is the definition of an answer?
    >I don't think that this question has been satisfactorily answered.
    Indeed, and that may be the basic problem we are having here. Your 
    idea of answer apparently differs from Ian's, for example.
    My own view on this is that there is no *definition* of an answer, 
    but there are some conditions that all answers must satisfy. The only 
    condition that everyone will likely agree on is that any answer must 
    be entailed by the KB. (That is, that the instance of the query with 
    that binding is entailed by the KB.)  I think in fact that this is 
    *all* that should be required in a spec., and that any attempt to 
    ensure that 'all' answers are given, or that logically equivalent KBs 
    must give identical answers, are misguided in the SW context; they 
    are far too strong to permit implementors to experiment, so will in 
    fact simply be ignored in practice; and in any case I do not think 
    that they are sensible in a Web open architecture. So I'm afraid that 
    I find this debate somewhat pointless and timewasting.
    Assuming that we do want to define something like the 'answer set' (I 
    would like to see some rational explanation for why this concept is 
    useful, by the way) , Ian has argued strongly that it should not 
    include all 'answers' that can be logically inferred from the KB, but 
    only those which arise from a binding of a query variable to a term 
    in the KB Herbrand universe, in order to keep the inferential burden 
    on the server within DL-manageable bounds. I am happy with that; but 
    given the resulting incompleteness, it seems silly to object to a 
    proposal on the grounds that logically equivalent KBs may not always 
    deliver the same answers.
    The point of the MID construction was to provide some useful 
    information to the querying system in the case where a binding itself 
    provides no useful information. We can debate the technical details 
    of how best to do this, but that some such mechanism is needed seems 
    to me to be obvious. In particular, any proposal for defining 
    'answer' which arbitrarily forbids a server from transmitting useful 
    information to a querying engine, when it has already had to compute 
    that information in order to answer the query, seems to me to be so 
    mind-blowingly stupid as to not be worth discussing further.
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