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Figure 7.2
Elixir CASE
Types of Associations on a Class Diagram
An Aggregation is a special form of association that specifies a part-of
relationship. It implies a constraint on the life-span of the component part.
For example, a book is part of a library.
A Containment relationship is a stronger variation of the aggregation
relationship. In a containment relationship, the part object is meaningless if it
does not belong to only one whole object. In addition, deletion of the whole
object means that the part is also deleted with it. A book and a page have a
containment relationship; a book contains pages and destruction of the book
destroys the pages as well. Also, the book knows its pages, indicated by the
arrow from book to page, as shown in Figure 7.2.
Extends
An Extends relationship is equivalent to the inheritance relationship. It is a
taxonomy relationship between a more general element and a more specific
element. The more specific element is fully consistent with the more general
element and contains additional information. An instance of the more specific
element may be used where the more general element is allowed. For
example, a reference book is a kind of book, as shown in Figure 7.2.
How To Create A Class Diagram ?
Package
First, you may like to provide a package to contain the classes. We can do that using
the Package tool from the Toolbox to create a new package or to call up an existing
one.
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