- From: Pat Hayes <phayes@ihmc.us>
- Date: Mon, 31 Oct 2005 16:51:09 -0600
- To: Enrico Franconi <franconi@inf.unibz.it>
- Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>
>Hi Pat, >have you checked this document? What do you think? Can be a >reasonable starting point? >cheers OK, finally I am emerging from a pile of... never mind what the pile was a pile of. Some quick comments. 1. First, I think we can use this as a basis, yes, modulo some questions. Most of the comments are more to do with 'style' than actual content. 2. I would prefer to not use translations to 'external' logical forms, as in your definition 3, unless they are absolutely necessary (and I don't think they are). The RDF documentation should provide enough terminology to do most of this, I think. In fact, I have trouble following definition 3, particularly that of L(AS). What is the purpose of introducing the relation R at all? Since the definition refers to logical equivalence, and R is an arbitrary nonlogical formula, the logical redundancy can only arise from a structural redundancy, i.e. an instantiation of bnodes producing an identical pattern substitution. This could be stated directly, and would IMO be far clearer. So: an instance mapping is a function from bnodes to RDF terms (previous definition in RDF), and a pattern solution is a partial function from V to RDF terms (definition 2). A set of answers is redundant when there are answers A1 and A2 in it such that for some instance mapping I, A1 = A2oI, where o is functional composition; that is, speaking loosely, when one answer A1 is an instance of another answer A2, which we will call a redundant answer. 3. RDF merge is already defined, but your definition adds an ordering requirement on the bnode re-namings. Is that important? 4. We have to rephrase definition 5 because of course an RDF graph does NOT contain query variables, but that is just wording. 5. In definition 6, line 4, should be G |= (G U Q[s]) rather than G |= (G U Q)[s] (??) 6. I don't want to say or imply that the list of four entailments are the only possible well-defined entailment relations. Also, Im not sure what 'well-defined' means here. 7. (Substantive). Why, in line 2, are the bnodes in the range of S restricted to bnodes in G? Surely it should be possible for an answer service to use 'new' bnode labels in an answer? I see no need for this restriction on bnodes, in any case. 8. Is Lemma 1.3 really correct? The query might fail to notice the structure which keeps the graph lean. For example, the query ?v ex:p ex:a against the lean graph {ex:b ex:p ex:a _:1 ex:p ex:a _:1 ex:q ex:c} will produce the answers ?v/ex:b and ?v/_:1, which I think are redundant by your definitions, no? (If not, please explain what I have missed in the definition of redundancy, which as I said I have trouble following in detail.) 9. I do not understand the terminology used in lemma 1.4. What is a subgraph isomorphism? What is a projection over bnodes? What is the query variable of an isomorphism? Is it possible to express these ideas using existing terminology, rather than inventing new terms that need to be defined? ------- OK, more later, but this will get us started. Pat >--e. > >On 24 Oct 2005, at 21:10, Enrico Franconi wrote: >>Hi, >>we have tried to summarise the discussions on the semantics of the >>last month in a document [1], which presents the very abstract >>semantics of SPARQL. By now, it focuses mostly on basic query >>patterns, but we will expand it further to cover the algebra as >>well. We hope that we can agree on this first part soon, so that >>this can be the basis for the official documents. >>Comments are very welcome and desirable! >>cheers >>--e. >> >>[1] The Semantics of SPARQL <http://www.inf.unibz.it/krdb/w3c/sparql/> -- --------------------------------------------------------------------- IHMC (850)434 8903 or (650)494 3973 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32502 (850)291 0667 cell phayesAT-SIGNihmc.us http://www.ihmc.us/users/phayes
Received on Monday, 31 October 2005 22:51:30 UTC