# Re: Cardinality - I really need help

From: beginner16 <kaja_love160_at_yahoo.com>
Date: Wed, 08 Aug 2007 13:24:10 -0700
Message-ID: <1186604650.113782.105960_at_19g2000hsx.googlegroups.com>

hello

On Aug 5, 10:02 pm, Hugo Kornelis
<h..._at_perFact.REMOVETHIS.info.INVALID> 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 Received on Wed Aug 08 2007 - 22:24:10 CEST

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