Path: newssvr20.news.prodigy.com!newsmst01.news.prodigy.com!prodigy.com!pd2nf1so.cg.shawcable.net!residential.shaw.ca!peer02.cox.net!cox.net!newsfeed2.easynews.com!newsfeed1.easynews.com!easynews.com!easynews!news.he.net!chekhov.conxion.net!news.oracle.com!not-for-mail From: "Mikito Harakiri" Newsgroups: comp.databases.theory References: Subject: Re: Possible problems with Date & McGoveran View Updating Lines: 35 X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 6.00.2600.0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000 Message-ID: Date: Mon, 8 Sep 2003 19:17:56 -0700 NNTP-Posting-Host: 130.35.179.109 X-Trace: news.oracle.com 1063074414 130.35.179.109 (Mon, 08 Sep 2003 19:26:54 PDT) NNTP-Posting-Date: Mon, 08 Sep 2003 19:26:54 PDT Xref: newssvr20.news.prodigy.com comp.databases.theory:21355 "Bob Badour" wrote in message news:N3b7b.732$%Q.69880903@mantis.golden.net... > > Not general enough. > > Not general enough for what? Clarified in different thread. > > Constraints are one possibility. Extending views (aka adding more > equations) > > like in the "union" example above is more general approach. > > The view is what it is. Extending the view would alter the logical view of > some user or application. No, I'm not suggesting to arbitrarily extend the view. The system must just reject any attempt updating ambiguous system of views. The user can correct the error by supplying view update effect on additional views (which is analogous to adding more equations). If you agree that constraint is a view that evaluates to a constant, then you can easily adopt the idea that there are multiple views involved, not just one. At least, one view with input and output relation variables V*x=y and many constraints like this VC*x=DUM Next, I can hope handling equations involving views with a uniform method, while Date et.al. needs to a special rules involving constraints.