crow’s footĬrow’s foot notation isn’t the only way to draw an entity-relationship diagram. No more than one relationship is possible between instances.Īnother optional relationship, with a maximum of one. The “one” indicates that this is not an optional relationship, although there might be more than one. There might not be any connection between the entities, or there might be one or more. You can see from this line just where the name “crow’s foot” came from…Ī zero or many relationship means that it is optional. These indicators are shown on both ends of the relationship line so that you can see how the entities relate to each other. Note that most of the time you can just use the word cardinality. Modality tells you the minimum number of times that the instance can be associated with instances of the other entity. Cardinality tells you the maximum number of times that an instance of an entity can be associated with instances of the other entity. Relationship lines in crow’s foot notation have two indicators to describe the cardinality and the modality of the relationship. How do relationships work in crow’s foot notation? Cardinality and modality Relationships between entities are represented by a line with a verb written on the line. The entities depicted in the diagram have relationships that describe how they interact.

So our player entity is represented by a rectangle with the word player inside it. The identifier is shown with an asterisk next to its name. One of those attributes will be its key attribute, or identifier, which uniquely identifies that entity. An entity can have one or lots of attributes.

These attributes get listed underneath the name in the rest of the rectangle. AttributesĮntities have attributes that describe them. EntitiesĪn entity is a real-world thing (person, place, object – whatever you can name in your database can be an entity) represented in crow’s foot notation by a rectangle with a name in a box on top. What are the symbols used in crow’s foot notation?Ĭrow’s foot notation uses some unique shapes and symbols to represent the elements in a database.

Crow zero 3 pictures