Path: news.easynews.com!core-easynews!newsfeed3.easynews.com!easynews.com!easynews!news.glorb.com!newsgate.cistron.nl!transit.news.xs4all.nl!not-for-mail Date: Sun, 06 Jun 2004 16:21:28 +0200 From: mAsterdam User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.6) Gecko/20040113 X-Accept-Language: nl, is, fr, de, en, en-us, ja, ko, zh MIME-Version: 1.0 Newsgroups: comp.databases.theory Subject: Re: cdt References: <40c30358$0$568$e4fe514c@news.xs4all.nl> In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Lines: 37 Message-ID: <40c32861$0$559$e4fe514c@news.xs4all.nl> NNTP-Posting-Date: 06 Jun 2004 16:21:21 CEST NNTP-Posting-Host: 194.109.233.75 X-Trace: 1086531681 news.xs4all.nl 559 [::ffff:194.109.233.75]:1811 X-Complaints-To: abuse@xs4all.nl Xref: core-easynews comp.databases.theory:35731 X-Received-Date: Sun, 06 Jun 2004 07:20:41 MST (news.easynews.com) Alan wrote: > Laconic2 wrote: >>Perhaps the problem lies in the word "implicit", in the term "implicit >>meaning". Perhaps what is implicit is subject to misinterpratation. > > Not if you know the difference between implicit and explicit, which you have > provided by example, below. Implicit is implied, explicit is expressed. > Implicit is correct in this case. I'm fairly sure Drs. Elmasri and Navathe > carefully considered which word to use, and that their editor reviewed it > somewhere during the process of creating three editions of the book. Try, > > Known facts that can be recorded and have _an implied_ meaning. > > They're not explicit until after they've been recorded (or stated, i.e., > expressed). > >>Back in the days before databases, when COBOL programmers stored data in >>records in files, the records had an "implicit" record definition. The >>COBOL programmer needed to include the correct record definition in the >>program in order to read the data. By including the data definitions in >>By including the data definitions in the >>schema, and putting the schema in the database, the definitions were made >>"explicit" rather than "implicit". Column names, table names hint at meaning, they do not really define. It does not help rephrasing this in relational terms: The names of attributes and relational variables don't do a better job at defining. The meaning of the propositions conveyed by the tuples is supposed to be explained by the *external* predicate (3rd manifesto, 1st edition). "external" suggests that the authors do not think of the predicate as being part of the database - but I can't check this as I don't have the book here. The "definitions" in the schema only serve to associate the structure of the relation body with the relation header.