From: Pat Hayes (phayes@ai.uwf.edu)
Date: 01/13/02
>In this message, I will reply to your comments on my overview of what's >in a query and in a query response. I will comment on your proposed use >of continuations in a following message. OK, and sorry the response is so late. Im catching up slowly :-) > > >WHAT'S IN A QUERY >> > >> >* Knowledge Base - I think we are all agree that a query is posed with >> >respect to a DAML+OIL knowledge base. Thus, a query needs to include a >> >reference to a DAML+OIL knowledge base. I am referring to that >> >knowledge base as the "query KB". >> >> It would make more sense to call it the 'server KB'. >> >> Do we in fact want to assume that there is a unique KB for each >> query? Eg consider a 'services' setting in which a query can be >> published, meaning 'any site that can prove this, give me an answer'. >> The RDF core WG considered such a possibility, where one might >> publish a piece of RDF that said, in effect, please prove that I can >> get flowers from you amounting to this quantity before this date at >> less than this price (and then you and I have a deal). >> >> This might well be a natural way to deal with 'queries', in fact, in >> a commercial B2B context; the logic is the same, so why not allow it >> as a possibility? In other words, such a publication is a kind of >> open-ended query in which the KB - ie the identification of the KB - >> is itself part of the answer. > >Interesting. I have been thinking of a query as asking what is entailed >by a given logical theory. Right, me too. >I think you are suggesting that we expand >that notion to include asking what is true in some domain of discourse >like our consensus reality. Well, you might phrase it that way, but what I had in mind was something more restricted, ie allowing logical theories to choose themselves to 'match' a query. >That would mean, for example, that a query >could ask "Who is the Chief Justice of the U.S. Supreme Court" (to take >a random example), or as you suggest, ask a query about a Web service. >If we do that expansion, what constitutes a correct answer to such a >query. Well, the answer is still what it was before, but now it includes a specification of the KB that is providing the answer. The only difference is who chooses the KB: is the query always directed to a particular KB, 'chosen' by the query itself, or can a query be directed to a community of KBs, and thereby invite many, possibly different, responses? >What if a server said that I was Chief Justice of the U.S. >Supreme Court? Well, if that is what it said, then it could presumably be held responsible for any valid conclusions from that assertion. >When a query is about entailment in a given logical >theory, we know what the test is for correctness of an answer. I wasn't suggesting changing that, only allowing the query to be answered by several different 'theories'. This is a web context, after all, and presumably we have to expect that there will be many ontologies in use. >I don't >know what a query is about when it is not with respect to a given >logical theory. Well, it is exactly the same, but it invites any theory to prove it. The logic is the same. >Of course, an easy case is where a knowledge base is >not specified in the query but is specified in a query answer so that >the answer specifies a sentence that is entailed by the knowledge base >that is referred to in the answer. Right, exactly. That is what I was suggesting. > >> >* Premise - I have proposed that a query optionally include a premise to >> >facilitate if-then queries while still remaining within the >> >expressiveness of DAML+OIL. Specifically, I have proposed that a >> >premise be an arbitrary DAML+OIL knowledge base. There has been no >> >formal agreement on whether or not DQL will allow a "query premise". >> >> I would vote not, in the first draft. It smacks of tiptoeing into >> 'rules' territory, and it ought to be definable in any case by >> querying a KB containing the premise and an import of the previous KB. > >Well, we have discussed this before. Right, and I still think that the answer should be not, in the first draft. I would like to keep the query language as simple as possible at first, and solve the problems a few at a time. > The primary motivation is to allow >queries to be stated using only DAML+OIL (no rules) that hypothesize and >describe objects and then ask a question about the hypothesized objects. That seems like a potential minefield to me, and one that we should venture into carefully. > >> >answer will include a binding for each distinguished variable. I am >> >referring to the variables in the query pattern that are not >> >distinguished variables as "non-distinguished variables". >> >> undistinguished variables? > >From a quick check on the Web, I find them being called >"nondistinguished variables". > >> >WHAT'S IN A QUERY RESPONSE >> > >> >* Query - The query to which this is a response. >> > >> >* Server - The server that produced this response. >> >> ? This seems rather like having a piece of code sign its name to >> everything it does. Surely, if I am querying a KB, I already know >> what the query was. Why do I need to be told this again? >> >> BUt in any case, what exactly *is* the 'server' here? You seem to be >> assuming that servers are genuine things on the web, but that seems >> to be something that we havn't really decided on yet. How does DAML >> refer to agents, so it can express this response? (Or indeed to >> queries, for that matter)? > >I was assuming that a server has a URI. OK. But then we need on ontology of servers, right? > >I suppose it is not critical that a query response contain a pointer to >the query to which it is a response, but it certainly needs to contain a >pointer to the server, since the answers contained in a response are >server-specific in that those are the answers that that server did >produce to the query. (Yes, each answer is correct or not regardless of >who produced it, but the set of answers is server-specific in that those >are the ones that were produced by the server out of all the possible >correct answers.) > >> >* Answers - Zero or more answers to the query. >> >> Right, but how is 'zero answers' indicated? > >I don't see that as being a problem. A query result would necessarily >have some sort of collection (e.g., a list) of query answers, and if >there are zero answers then that collection would be empty. OK again. Pat -- --------------------------------------------------------------------- IHMC (850)434 8903 home 40 South Alcaniz St. (850)202 4416 office Pensacola, FL 32501 (850)202 4440 fax phayes@ai.uwf.edu http://www.coginst.uwf.edu/~phayes
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