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Entity Relationship Modeling


Entity Relationship Modeling (ER modeling) is by far the most common way to express the analytical result of an early stage in the construction of a new database. In this ebook, Alf Pedersen describes the principles for ER modeling, as well as the most important terms used in modeling a new database.

Author Info:
By: Alf A. Pedersen
Rating: 4 stars4 stars4 stars4 stars4 stars / 89
April 05, 2004
TABLE OF CONTENTS:
  1. · Entity Relationship Modeling
  2. · The Entity
  3. · Other Business Contacts
  4. · Attributes in entities
  5. · Business Rules
  6. · Three types of relationships
  7. · Supplier Entity
  8. · A Weak Relation
  9. · A Useful Relation
  10. · Involuted (or recursive) relationships
  11. · Many-to-Many
  12. · The Database Analysis Team - A Teamwork
  13. · Level of Knowledge
  14. · Experience vs. Inexperience
  15. · Complete Model?
  16. · Building Queries
  17. · Other Common Errors in ER Modeling
  18. · Second Normal Violation
  19. · More Specific
  20. · Generic or Specific Models?
  21. · Analysts Experience

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Entity Relationship Modeling - More Specific
(Page 19 of 21 )


Now we can be more specific-

Entity Relationship Modeling

The model is still not complete since the Primary key definitions are insufficient. Also, the arc between business contact and shareholder has to be studied closer. Arcs are, in my opinion, a signal that the area is insufficiently studied. What we really say with an arc is- it's either this or that. Make a choice. That is not good enough, in my opinion. The only difference between any kind of business contact and a shareholder is that a shareholder owns one or more stocks in our company. Otherwise, he may be a customer, a supplier, or whatever.  

If we change the name of shareholder to stock, and we add a couple of attributes, and we define a primary key for contact role, we get-

Entity Relationship Modeling


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