Tips for creating an ERR Diagram — Design tips

Many of the tips that I am going to give are from this excellent book that I want to recommend:

Informal guidelines for relation design:

Tip 1: The schema design process should be considered an iterative refinement process

Tip 2: Proper Naming of Schema Constructs

Tip 3: Design choice entity type, attribute or relationship type

http://www.cs.toronto.edu/~jm/2507S/Notes04/EER.pdf

Tip 4: Choosing between Binary and Ternary…

Tip 5: Design Choices for Specialization/Generalization

Tip 6: The diagram should be connected, no part should be isolated

Tip 7: Test the relationships cardinality

  • Use extreme cases
  • Use 1:1
  • Other cases that must be true according to the description of the problem
  • Other cases that must be false according to the description of the problem

Tip 8: Test that the relationship has the correct degree

Make sure that you test is the relationship has the correct degree.

  • Test 1: Is it possible that there are more entities in a relationship instance than the degree of the relationship? If yes, then there is a problem
  • Test 1: Is it possible that there are fewer entities in a relationship instance than the degree of the relationship? If yes, then there is a problem

Take into account that:

  • If the is a relationship between 2 entities of the entity types, then unary
  • If the is a relationship between 2 entities of 2 different entity types, then binary
  • If the is a relationship between 3 entities of 3 different entity types, then ternary.

Tip 9: Identify the entity types, relationship types and attributes directly in the document with different colors

Example:

Other useful resources & link

https://vertabelo.com/blog/common-er-diagram-mistakes/