# cardinality

**Category:** [Implementers (archive)](https://discourse.openehr.org/c/implementers-archive/158)
**Created:** 2007-05-19 11:26 UTC
**Views:** 6
**Replies:** 4
**URL:** https://discourse.openehr.org/t/cardinality/14645

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## Post #1 by @system

I had one more question, I said this morning:

What is the use of the numerical part of the Cardinality object, I wonder?

It can be calculated from the number and occurences of the items\. Or do
I misunderstand?

For example

events cardinality matches \{\*;ordered\} matches \{
    EVENT\[at001\] occurences matches \{0\.\.1\} matches \{\*\}
    EVENT\[at002\] occurences matches \{0\.\.1\} matches \{\*\}
    EVENT\[at003\] occurences matches \{0\.\.1\} matches \{\*\}
\}

Because the attribute "events" can have 0 to 3 elements \(the occurences
property tells me\), the cardinality is \{0\.\.3;ordered\}
It cannot be something else\.

Or do I misunderstand?

Thanks in advance for an answer

regards,
Bert

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## Post #2 by @system

The use for the numerical part of Cardniality, I can think of, is

events cardinality matches \{0\.\.2;ordered\} matches \{
    EVENT\[at001\] occurences matches \{0\.\.1\} matches \{\*\}
    EVENT\[at002\] occurences matches \{0\.\.1\} matches \{\*\}
    EVENT\[at003\] occurences matches \{0\.\.1\} matches \{\*\}
\}

In this way teling that only 2 ELEMENT total may be in this list of events

Is that right

Bert

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## Post #3 by @Sam

Bert
That is right - it is the way of limiting the number of choices as you have said...Sam

Bert Verhees wrote:

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## Post #4 by @system

Sam Heard schreef:
> Bert
> That is right \- it is the way of limiting the number of choices as you
> have said\.\.\.Sam

Thanks, Sam, for the confirmation\.

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## Post #5 by @thomas.beale

Bert Verhees wrote:
> I had one more question, I said this morning:
>
> What is the use of the numerical part of the Cardinality object, I wonder?
>  

'cardinality' \(in ADL\) says how big the container can be \- imagine it is
like a box containing LEGO pieces\. 'occurrences' says how many of a
particular kind of object \- e\.g\. 8x2 LEGO bricks \- can be in the
container\. 'Existence' says if there is a container or not\. For
non\-container attributes, 'occurrences' always matches 'existence'\.

\- thomas

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**Canonical:** https://discourse.openehr.org/t/cardinality/14645
**Original content:** https://discourse.openehr.org/t/cardinality/14645