Path: text.usenetserver.com!out03a.usenetserver.com!news.usenetserver.com!in02.usenetserver.com!news.usenetserver.com!postnews.google.com!n60g2000hse.googlegroups.com!not-for-mail From: beginner16 Newsgroups: comp.databases.theory Subject: Bachman diagrams and E-R model Date: Mon, 23 Jul 2007 18:01:52 -0700 Organization: http://groups.google.com Lines: 31 Message-ID: <1185238912.812494.302130@n60g2000hse.googlegroups.com> NNTP-Posting-Host: 82.192.44.41 Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Trace: posting.google.com 1185238913 22670 127.0.0.1 (24 Jul 2007 01:01:53 GMT) X-Complaints-To: groups-abuse@google.com NNTP-Posting-Date: Tue, 24 Jul 2007 01:01:53 +0000 (UTC) User-Agent: G2/1.0 X-HTTP-UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.8.1.4) Gecko/20070515 Firefox/2.0.0.4,gzip(gfe),gzip(gfe) Complaints-To: groups-abuse@google.com Injection-Info: n60g2000hse.googlegroups.com; posting-host=82.192.44.41; posting-account=ps2QrAMAAAA6_jCuRt2JEIpn5Otqf_w0 Xref: usenetserver.com comp.databases.theory:165952 X-Received-Date: Mon, 23 Jul 2007 21:01:53 EDT (text.usenetserver.com) hello 1) When designing a database, we may use ( I=E2=80=99m not sure if at different or same stages of development ) each of the following three diagrams: - bubble diagram - e-r diagram - data structure diagram ( bachman=E2=80=99s diagram ) a) Are Bachman and bubble diagrams also used at conceptual level? b) So when do choose Bachman diagram, when bubble diagram and when E-R diagram? c) What are some major differences between Bachman and E-R diagrams? 2) My book claims that Bachman diagram only knows one-to-one, one-to-many and many-to-many relationships. But then how do Bachman diagrams graphically represent zero-to-many relationships? My question above is based on the assumption that 1:N relationship means that instance of entity type A can have zero, one or many connections to instances of entity type B, while each instance of entity type B must have exactly one connection to entity A =EF=83=A0 In other words, each instance of entity type B must have one ( zero connections is not allowed ) connection to instance of A entity. Am I correct? thank you