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Sunday, April 07, 2013


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Nice reference design, but:

What is the difference between:
[ENTITY]--|---- [one], (<--- This what confuses me against other two)
[ENTITY]-|0---- [zero or one], and
[ENTITY]-||---- [One and ONLY one]

Vivek M. Chawla

Typically, I've seen the use of the...

[ENTITY]--|--- (one)
[ENTITY]>--- (many)

...syntax on quick, "informal" Entity Relationship Diagrams. I wanted to paint a complete picture of what people might come across, so I added them to my Quick Reference chart.

The reality is that any relationship that has a direction ending in "one" should really be "zero or one", "one or many", or "one and only one". Same goes for "many", minus the logical absence of "many and only many", which doesn't exist.

Hope that helps clear things up!


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