Perhaps you, like me, were taught to use the Crow's Foot Notation when learning DB Modelling; perhaps you just like to use because you think it's the most straightforward and intuitive notation.
Either way, you can use MS Visio 2010 to create DB Relationship Diagrams with that.
When you've switched to the Software/Database modelling area, click the Database tab and then Display Options. A pop-up window will come up where you can set the notation style to "Crow's Foot".
zero or one
When a Car is first made, it has no owner, which is a Person. It will only have an owner when it gets sold. A Person, on the other hand, may own no Cars but may own many Cars if he/she buys them.
- a Car can have zero or one Person (in blue)
and a Person can have zero or more Cars
zero or more
When a Car is still being manufactured, it has no Tires. Tires will be added to the Car before it can be used. The Tire, just after being produced, is part of no Cars. However, when a Tire gets placed in a Car, it cannot, at the same time, be in another Car.
- a Car can have zero or more Tires (in blue)
and a Tire belongs to zero or one Cars.
Say you are building a blog system consisting of Articles and Persons, who author the Articles. Let's pretend each Article must have only one Author. There can be no Articles without authors. Each Person can, in turn, write as many Articles as he/she wants, but he/she may also choose to write no Articles. So:
- an Article has precisely one Person (in blue)
and each Person may write zero or more Articles.
one or more
Suppose now you have a system to manage Books and Chapters. Each Book needs to have at least one Chapter so that it can be considered a Book. On the other hand, each Chapter must belong to one Book, as there can be no "standalone" Chapters not belonging to a Book:
- each Book can have one or more Chapters
and each Chapter must belong to one and only one (i.e. precisely one) Book