Path: news.cambrium.nl!textnews.cambrium.nl!feeder3.cambrium.nl!feed.tweaknews.nl!postnews.google.com!l33g2000pri.googlegroups.com!not-for-mail From: vadimtro@gmail.com Newsgroups: comp.databases.theory Subject: Re: Date and McGoveran comments on view updating 'problem' Date: Fri, 12 Dec 2008 10:31:09 -0800 (PST) Organization: http://groups.google.com Lines: 34 Message-ID: References: <2ac2d60f-c6fe-41df-be7f-0af7e756f9a9@x8g2000yqk.googlegroups.com> <67b08aa0-8c23-482c-9f3a-c7c85bbb5ad4@d36g2000prf.googlegroups.com> <1834bcb1-8f5f-4a27-9e1a-98831b95c9e1@r10g2000prf.googlegroups.com> NNTP-Posting-Host: 70.137.179.95 Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-Trace: posting.google.com 1229106669 27370 127.0.0.1 (12 Dec 2008 18:31:09 GMT) X-Complaints-To: groups-abuse@google.com NNTP-Posting-Date: Fri, 12 Dec 2008 18:31:09 +0000 (UTC) Complaints-To: groups-abuse@google.com Injection-Info: l33g2000pri.googlegroups.com; posting-host=70.137.179.95; posting-account=dmGV1QoAAAD_iLea43F098rb5Yhuc0yg User-Agent: G2/1.0 X-HTTP-UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.0.4) Gecko/2008102920 Firefox/3.0.4,gzip(gfe),gzip(gfe) Xref: news.cambrium.nl On Dec 12, 3:34=A0am, JOG wrote: > Ah, of course, the header. Now it makes sense - distributivity > requires correspondence in header unions. It might be worth noting > that I did not make the assumption that headers intersect when the two > components of a join are disjunct (and on a quick reglance of your > work could see no mention of this). In "First Steps in Relational > Lattice" you very neatly define a natural join over two binary > relations as: > > A(x,y) ^ B(y,z) =3D {(x,y,z) | (x,y)EA & (y,z)EB } > > However, this makes no mention of headers at all, leaving ambiguity > that might be worth just rectifying in future papers (to avoid any > confusion in those like me who don't assume a theoretical requirement > for header constructs). I never realized that this set definition might be a stumbling block! Jan was criticizing this section of the manuscript as well. My line of thought was: "OK, everybody knows what natural join is, we don't need set definition for that. Inner union, however, is a new construct, so it has to be defined (in set notation). In case if a reader has a problem with inner union definition why not to provide a natural join definition? Then the reader can consolidate definition for familiar operation with his notation confusion". It looks like this idea didn't work:-) > Nevertheless all very interesting stuff Vadim! Have you formally > published your work in this area? Alas, just missed PODS deadline http://www.sigmod09.org/calls_papers_important_dates.shtml by couple of days!