I'm trying to understand the proper use of optionality on potentially both sides of a relationship. Example:

Entity A has zero, one, or many entity Bs. I'm thinking this would be drawn as:

A --------o< B

... rather than:

A -o-|----o< B

... because the "o" on the right side fully explains that there may be no related items.

My hunch is also that the "|" on the left side, alone, would not be necessary, since an unadorned line on the left means 1:

A -|------o< B

I thought I'd ask here.

Bob

Entity A has zero, one, or many entity Bs.

This would be drawn as:

A ?? --------o< B

What to draw on the side closer to A depends on how many A's can a B have - and you haven't said anything about that.

0 or 1. I was thinking that:

A ---

... was a simplified way of describing that A cannot have many (that it would be 0, or 1). Would you then suggest this way of drawing it?:

A -|-o----o-< B

Thanks,

Bob

Yes. See also:

http://www2.cs.uregina.ca/~bernatja/crowsfoot.html

BTW, modality is less critical than cardinality, esp. if you are going to implement in Filemaker. IMHO, an ERD using only

A ----< B

notation to indicate a one-to-many is quite sufficient to convey the intended meaning.

BTW, modality is less critical than cardinality, esp. if you are going to implement in Filemaker. IMHO, an ERD using only

A ----< B

I just read that in the FM Training Series book. Thanks also for the url, very useful.

Bob

I just read that in the FM Training Series book.

How's that possible? I only wrote it like an hour ago... :P