Path: news.easynews.com!newsfeed1.easynews.com!easynews.com!easynews!newsfeed.news2me.com!newsfeed-west.nntpserver.com!hub1.meganetnews.com!nntpserver.com!telocity-west!DIRECTV!sn-xit-03!sn-xit-01!sn-post-01!supernews.com!corp.supernews.com!not-for-mail From: Phil Singer Newsgroups: comp.databases.theory Subject: Re: Other tree representations in SQL Date: Wed, 11 Dec 2002 23:27:44 -0500 Organization: orecreeksystems Message-ID: <3DF81040.CD7CD39@chartermi.invalid> X-Mailer: Mozilla 4.05 [en] (Win95; U) MIME-Version: 1.0 References: Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Complaints-To: abuse@supernews.com Lines: 29 Xref: newsfeed1.easynews.com comp.databases.theory:24058 X-Received-Date: Wed, 11 Dec 2002 21:19:12 MST (news.easynews.com) Carl Rosenberger wrote: > > (2) All object databases products with noticeable market > share between 1980 and 2000 were transparent persistency > systems. Transparent persistency can only work in > concurrent-multi-user environments, if a "read back in > time" isolation level is provided. As far as I am informed, > none of the available "best selling" products has this > feature. Instead they still work with read locks to ensure > consistent objects. > ...so they are still not ready for prime-time today. > Oracle 9 (available for 2 years now) does allow for a complete read-back in time, that is, one can query the database for a table as it existed at a specified time in the past. Depending on exactly what is meant by "transparent persistency", Oracle may have had this feature for the last 12 years. Certainly, for at least that time, the Oracle Mantra "reads don't block writes, and writes don't block reads" has been true. -- Phil Singer | psinger1ATchartermiDOTnet Oracle DBA