So the in the last blog article cardinalities were the subject. Therefore we’ll look into how to formally express the type of cardinality in a diagram here. Each type has its own notation which can resemble feet of a crow hence the notation’s name.
There are several different ways of symbolizing relationtypes. Have a look here if you want to know more:
https://en.wikipedia.org/wiki/Entity–relationship_model#Related_diagramming_convention_techniques
As the title of this article also revealed this will be about Crow's foot or Martin notation. The basic types of cardinalities of the last article are expressed as follow in the crow’s feet notation:
- ONE-TO-ONE
- MANY-TO-ONE
- MANY-TO-MANY
This notation has simple elements. When a relationship exists between tables a simple line is drawn between them.
Then at each end of the line symbols are added for whether one or more entities are present at this end of the relationship.I simplified the diagram for now since it can contain more symbols on the line. In short, one entity is symbolised by a small vertical line.
On the other side when many entities are present they are symbolised by an arrow which points towards the middle.
And there we have it, a first approach on how to formally express cardinalities or relationships between different tables.