sql server programming: 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)


[quoted text, click to view]

Cardinality tells a number of connections certain occurrence of entity
type can have with instances of some other entity type.

a)
Here is a picture from my book:

http://s195.photobucket.com/albums/z194/beginner16/?action=view&curre...

Book claims symbols on the graph show cardinality of E2 --> E2 = (0,
1). Huh?! Symbols on a graph show that E1 instance can be connected to
zero or one instance of E2, so shouldn't cardinality of E1 be (0,1)?

b)
We have two entity types A and B:
A1 is an entity instance of type A
B1 is an entity instance of type B

As far as I understand cardinality, if we have two entity types A and
B, and if A1 can be connected to one or more instances of type B,
while B1 can only be connected to zero or one instances of A entity
type, then relationship is 0:N, as depicted in a picture:

Thus to my understanding:
* Cardinality of A1 = (1:N), where 1 tells minimum number of
connections ( of some type ) that A1 must have, while N tells max
number of connections.

* Cardinality of B1 = (0, 1)

But the following suggests differently:

[quoted text, click to view]

If I'd go by the quote above, then cardinality of A1 = (0, 1) and of
B1 = (1, N), which doesn't make sense!

thank you

[quoted text, click to view]

Hi beginner16,

Replied in comp.databases.theory.

Please don't post the same message independantly to multiple newsgroups.
Either pick a single group, or -if you really think the message belongs
in more than one group- post a singly copy to multiple groups at once.
That way, answers will also show up in all groups, saving people time
answer a question that was already answered elsewhere and keeping the
discussion coordinated.

--
Hugo Kornelis, SQL Server MVP

On Aug 5, 10:37 pm, Hugo Kornelis
[quoted text, click to view]

I apologize for that. In my defense, I thought this was kind of
confusing topic and the more heads the better I would understand such
a confusing topic. I hope you won't think that making same threads is
something I do on regular basis, since that is not the case ( though I
think I did this once before )

Again, sorry for any inconveniences I might have caused

cheers