Aggregate Relations
I’m tempted to say that aggregation is a stronger form of acquaintance, and that wouldn’t be far from wrong. In fact, in certain contexts it may be perfectly correct. Gamma, et al point out that the differences between the two is a matter of intent rather than explicit language mechanisms. That makes it a little tricky simply to show some code and pronounce, “See that’s what an aggregate looks like.” So bear with me as we look at aggregate relations.
Conjoined Participants
As can be seen in the red arrow symbols in the Participant Relations diagram at the top of this post, an aggregate relation is indicated by an arrow with a diamond at its base. The GoF illustrate the relationship as shown in Figure 1:
Figure 1: Aggregator and Aggregatee
The Aggregator creates an aggregate instance of the Aggregatee. As noted, GoF point out that no single code set can demonstrate what an aggregate relationship looks like, but I think that we can get a start by looking at a fairly simple relationship in the State design I created so that we could discuss both aggregate relations and delegation. (The Strategy design also provides a good example of aggregation with delegation.)
Continue reading ‘ActionsScript 3.0 Design Pattern Relations Part II: Aggregation’
Bill Sanders
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