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Preparation for colstruction 2


Notes:

We study the remainder of section 3.2 by the next colstruction. We do it by the colstruction because there is no labsession the week before easter.
In section 3.2.3 some additional operators are introduced. Let us briefly mention two of them:
The Join operator is very useful because it lets us use the connection between two tables through a common attribute. We have noticed today that we often need to combine a cartesian product with a selection on the common attribute. The join operator provides us with a more compact way to do this.
The Division operator is a very special one that lets us perform a selection based on sets. Exercise 3.5h can be expressed quite easily using the Division operator.