Re: Entity Relationship Diagrams

On 2007-04-11, Gregc. <gregchilton_at_bigpond.com> wrote:
> Hi
>
> I am currently drawing and ER diagram and am not sure about how to
> draw the diagram for the following: A bike must have at least 2 wheels
> but it may have more. The way that I would draw it is thus:
>
> BIKE-------< WHEELS (ie crows feet with no line)
>
> Would anyone have a suggestion on this.

The ER diagram is a communications tool. The first question to ask before trying to communicate, is precisely who you are going to be communicating with. If you are going to use the diagram to communicate with people you know, then the best notation to use is probably going to be whatever they already understand. Has anyone at your site already done this sort of thing before, if so what notation did they use?

If not then it may be best to find a reference work and base your notation on it. There are several methodologies that use slightly different ER notations. Pick one and stick to it. If you have a reason to deviate from the standard then write down what you did and why, and turn it into a company standard.

What you choose to do is partly dependent on the size of the shop. If you are head-cook and bottlewasher in chief then all you need to do is to leave a note so that if you get hit by lightning on the golf-course someone can pick it up and take over. If you are in a growing company and expect to hire more designers then you need a more rigorous documentation procedure because you don't know who will have to use the documents you produce.

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