Path: text.usenetserver.com!out04a.usenetserver.com!news.usenetserver.com!in02.usenetserver.com!news.usenetserver.com!postnews.google.com!19g2000hsx.googlegroups.com!not-for-mail From: beginner16 Newsgroups: comp.databases.theory Subject: Re: Cardinality - I really need help Date: Wed, 08 Aug 2007 13:24:10 -0700 Organization: http://groups.google.com Lines: 67 Message-ID: <1186604650.113782.105960@19g2000hsx.googlegroups.com> References: <1186255408.948471.113990@d55g2000hsg.googlegroups.com> <5facb3prbe163g1a1nih9baia7cppfq9d8@4ax.com> NNTP-Posting-Host: 82.192.44.41 Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" X-Trace: posting.google.com 1186604650 9225 127.0.0.1 (8 Aug 2007 20:24:10 GMT) X-Complaints-To: groups-abuse@google.com NNTP-Posting-Date: Wed, 8 Aug 2007 20:24:10 +0000 (UTC) In-Reply-To: <5facb3prbe163g1a1nih9baia7cppfq9d8@4ax.com> User-Agent: G2/1.0 X-HTTP-UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.2; en-US; rv:1.8.1.6) Gecko/20070725 Firefox/2.0.0.6,gzip(gfe),gzip(gfe) Complaints-To: groups-abuse@google.com Injection-Info: 19g2000hsx.googlegroups.com; posting-host=82.192.44.41; posting-account=ps2QrAMAAAA6_jCuRt2JEIpn5Otqf_w0 Xref: usenetserver.com comp.databases.theory:166152 X-Received-Date: Wed, 08 Aug 2007 16:24:10 EDT (text.usenetserver.com) hello Sorry for not replying sooner, but I just started learning Smalltalk and it kind of a drag. Anyways, I hope someone will still read this reply... On Aug 5, 10:02 pm, Hugo Kornelis wrote: > On Sat, 04 Aug 2007 12:23:28 -0700, beginner16 wrote: > >hello > > >I would really need some help here > > >Some time ago I made a thread about cardinality and thought I > >understood it , but today I noticed that I actually misread a post > >explaining cardinality and realized that the subject still very much > >confuses me. Below are the original question and a reply ( the one I > >misread) > > (snip) > > Hi beginner16, > > I've used various methods of entitytype relationship diagramming, and > there are many different to depict cardinality - one of the major > problems when switching between diagramming styles, as that some will > depict minimum and maximum cardinality on one side of a relationship, > others on another side of a relationship, and then there are some that > depict minimum cardinality on one side and maximum on another side!! > > Your model looks familiar, though I don't recall at the moment how the > diagramming style was called when I learned it. Anyhow, if this is the > style I think it is, than the information in your picture says that: > > - Each E1 is associated with at most 1 E2, as indicated by a vertical > bar instead of a craw paw (is that the correct English translation?) at > the E2 side of the line (maximum cardinality); and > - Each E1 does not have to be associated with any E2, as indicated by a > circle rather than a vertical bar at the E2 side of the line (minimum > cardinality); > > Since there is neither a vertical bar nor a craw paw, and neither a > vertical bar not a circle at the reserved spots at the E1 side of the > line, nothing is known about how many E1 may or must be associated with > any given E2. > > You may have noticed that I did not phrase any of these cardinalities as > being a cardinality "of E1" or "of E2" in this relationship, since the > interpretation of the term "cardinality of E1" tends to be as ambiguous > as some diagramming styles. > > Best, Hugo Anyways, I thought that a term cardinality always means the same, regardless of diagramming style used. I can see how one diagramming styles may put min and/or max cardinality on one side and others on other side, but I assumed that the term itself always means max and min number of connections an entity ( call this entity A ) of certain type can have with other entities --> so if A can have min zero and max one connection with B entity, then cardinality of A is (0, 1). I find it hard to believe, that depending on diagramming style, we would say that cardinality of B is (0, 1) thank you