Answer to Problem 1.4

The relationship between department and a managing employee is different than the one between division and department. It doesn't say so but we can assume that a department has only one manager.

An aside: Certainly you can imagine an instance in which a department has co-managers. That possibility is just as viable as the possibility I have assumed. This is part of the attraction of this type of work. The database professional has to read descriptions for what is said and then imagine what isn't said. If you were actually creating a database in this example, you would have to ask someone what the situation actually is. But since you are just given this description, you have to come up with some assumption. For this situation we'll make the above assumption.

We'll also assume that an employee can also be the manager of, at most, one department. In other words, for every one department there can be, at most, one managing employee. In the language of ER modeling this is called a 1:1 (read: “one to one”) relationship.

Return to simple modeling exercise.

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