Study Cards on attribute, multiplicity, editor
When we read the attribute with the multiplicity, we can say, “There are ONE OR MORE authors” or “There is at least one author.”
When there is a lower-bound and an upper-bound for a multiplicity,
it is a requirement that Lower-bound ≤ upper-bound
In the previous figure, we might have assumed that we would use “Anonymous” as the author of a book without authors.
More likely, the display software would automatically know that an empty author name should be displayed/printed as Anonymous.
Now examine Fig. 10.4.
This figure is equivalent to the previous Fig. 10.3.
What does only the * means?
In Fig. 10.6, we restored the default format of Fig. 10.5.
We also added the constraint on the number of pages as discussed above.
In Chapter 6, Objects and Classes, we showed several alternative forms for indicating the constraint.
Another approach would be
pages :Integer {in 1..*}
while multiplicity is surrounded by ?
In this constraint, we also use the ? that indicates a UML range.
while multiplicity is surrounded by [].
In this constraint, we also use the “..” that indicates a UML range.
This attribute also has the type of Person.
The multiplicity is shown as [0..1], indicating that the field is either there or not.
Some books do not have an editor.
We can say, “The editor attribute is optional” or “The Book MAY have an editor.” “May” is used to indicate that the lower bound is 0.
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