- From: Howard Katz <howardk@fatdog.com>
- Date: Fri, 16 Apr 2004 16:20:39 -0700
- To: "Eric Prud'hommeaux" <eric@w3.org>
- Cc: "RDF Data Access Working Group" <public-rdf-dawg@w3.org>
OK, I have a better idea of what you mean now. There is a standard mapping in the sense there's the SQL/XML work I referenced earlier [1]. I'm not a SQL person, so I don't feel I can speak very authoritatively on the ramifications of doing that. At a minimum I guess you'd have to not mind having to implement your RDF store in somebody's SQL db. (Does that parse?) It's certainly not a general-purpose solution. Howard [1] http://www.acm.org/sigmod/record/issues/0206/standard.pdf > -----Original Message----- > From: public-rdf-dawg-request@w3.org > [mailto:public-rdf-dawg-request@w3.org]On Behalf Of Eric Prud'hommeaux > Sent: Friday, April 16, 2004 11:40 AM > To: Howard Katz > Cc: RDF Data Access Working Group > Subject: Re: Supplemental XQuery reading list > > > > On Fri, Apr 16, 2004 at 07:54:06AM -0700, Howard Katz wrote: > > > > > > > I can't speak to Andy's agenda, but one point that's been kicking > > > around in the XQuery/RDF Query arena for a while is that XQuery can be > > > used to express SQL queries so it must be able to express RDF > > > queries. > > > > It can, if you're able to work out a mapping from the RDF data > model into > > the XQuery data model, which is basically the XML Infoset + XML Schema > > support + support for multiple documents. > > > > I'm finding myself quite interested in the inverse problem: would it be > > possible and useful to be able to map from the XQuery surface > language into > > an underlying RDF graph-based data model, so that XQuery syntax > can be used > > to interrogate an RDF data store more or less directly? In > other words, can > > we swap out XQuery's underlying XML-based data model and slide in an > > RDF-based one in its place so that we don't have to do the > mapping to XML? > > I'll be talking about this after Amsterdam. > > > > > I've seen a couple approaches that I believe workable [1] > > > [2], but would like to see how people solve the problem for SQL. > > > > I've given a few pointers in my response to Andy's email re SQL-to-XML > > mappings for XQuery. > > > > > I suspect that in standardizing an RDF query language we are going > > > beyond where existing SQL mappings to XQuery have gone in that we want > > > *one* mapping to XQuery that operates on XQuery+whatever > > > implementations from different vendors. Does such a "standard" mapping > > > to SQL exist? > > > > I'm not sure what you mean by the last, Eric. Can you explain a > bit more? > > Sure. One objection to using XQuery for querying RDF is that the data > models are different. In my view, this doesn't preclude its utility > but may force an awkward interface. One can invent conventions/ > libraries to access the parts of the SQL or RDF model with queries > that parse syntactically as XQuery (though this may be like mixing a > martini with a spatula). > > To prove the point, I was looking for a published or coded "standard" > that would enable some idiom of XQuery to access to any relational > database. Suppose I need to use up some asparagus and I use this > mythical "standard" XQuery mapping for relational databases > LET $r := document("odbc://localhost/db") > FOR $recipe in $r[table="recipies"], > $supplies in $r[table="supplies"] > WHERE $supplies/primaryKey=$recipe/ingredients > and $supplies/name="asparagus" > RETURN $recipe/name > to access a data base of two (poorly normalized) tables: > recipies: > name ingredient optional > cold cereal 3 > cold cereal 7 1 > steamed asparagus 14 > steamed asparagus 33 > > supplies: > primaryKey name > 3 dry cereal > 7 milk > 14 asparagus > 33 steam > > That was just to frame what I meant by a convention or standard for > accessing relational databases. If we want to use that for DAWGQL, > we could construct queries like > LET $t := document("odbc://localhost/db") > FOR $whoArc in $t[table="triples"], > $emailArc in $t[table="triples"] > WHERE $whoArc/predicate="<http://xmlns.com/foaf/0.1/name>" > and $whoArc/object="'Bob Smith'" > and $emailArc/subject=$whoArc/subject > and $emailArc/predicate="<http://xmlns.com/foaf/0.1/mbox>" > RETURN $emailArc/object > to execute a typical graph query (John Smith's email addr) on a > table of RDF triples called triples. > > Then the DAWG could define a the XQuery mapping of the DAWGQL in > terms of > 1 Use the Foo SQL-XQuery mapping spec. > 2 All triples are in a table called "triples" which has > the fields "predicate", "subject", "object". > We probably wouldn't want to, but it would be worth looking at. > > BTW: I refer to DAWGQL *because* it's such an ugly name that it > would never be used for anything but a placeholder. > > > > [1] http://www.w3.org/2001/11/13-RDF-Query-Rules/#XQueryFA > > > [2] http://www.w3.org/2001/11/13-RDF-Query-Rules/#TreeHugger > > > -- > > > -eric > > > > > > office: +81.466.49.1170 W3C, Keio Research Institute at SFC, > > > Shonan Fujisawa Campus, Keio University, > > > 5322 Endo, Fujisawa, Kanagawa 252-8520 > > > JAPAN > > > +1.617.258.5741 NE43-344, MIT, Cambridge, MA 02144 USA > > > cell: +1.857.222.5741 (does not work in Asia) > > > > > > (eric@w3.org) > > > Feel free to forward this message to any list for any purpose > other than > > > email address distribution. > > > > > -- > -eric > > office: +81.466.49.1170 W3C, Keio Research Institute at SFC, > Shonan Fujisawa Campus, Keio University, > 5322 Endo, Fujisawa, Kanagawa 252-8520 > JAPAN > +1.617.258.5741 NE43-344, MIT, Cambridge, MA 02144 USA > cell: +1.857.222.5741 (does not work in Asia) > > (eric@w3.org) > Feel free to forward this message to any list for any purpose other than > email address distribution. >
Received on Friday, 16 April 2004 19:19:28 UTC