Entity-Relationship Diagrams

I tend to forget what the arrows mean in an entity-relationship diagram.

Example

In the diagram above, there's strong limitations on the values possible in the GuildMember table. Unfortunately, these cannot be expressed in Foreign Key Relationships.

For example:

• a Person can hold only one rank in a Guild.
• a Person can only be a GuildMember in a Guild once.

The way to fascilitate this, is to put a unique index on GuildMember regarding the columns GUILDNR and PERSONNR.

References

PlantUML - Entity Relationship Diagram

https://plantuml.com/ie-diagram

LucidChart - Wat is een Entity Relationship Diagram?

https://www.lucidchart.com/pages/nl/wat-is-een-entity-relationship-diagram