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.
Entity Relationship Modeling - More Specific (Page 19 of 21 )
Now we can be more specific-
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-