Re: Cardinality - I really need help

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 Received on Sun Aug 05 2007 - 22:02:44 CEST