Access Interaction

Access interactions are used when an object needs information about another object. There are several ways to depict this information as shown in figures one through three.

In this section we will use the example of an Animal Feeder. We assume that at some point an animal feeder needs to access information on an animals' special diet or eating habits.

Figure 1 shows this interaction diagrammed as 2 separate interactions. First, the Animal Feeder requests the information from the high level object class Animal Care Information. The To: clause insures that the object containing the necessary information receives the interaction. This object responds by returning the diet for the specified animal.

Figure 1 - Representing access as 2 interactions

Since this type of interaction occurs frequently, figure 2 illustrates a shorthand notation. First, a bidirectional interaction is used instead of 2 interactions. Second, since the access interaction is, by default, returning the requested information, specifying what is requested in the interaction and the return list is redundant. In this example, exactly what information is requested is indicated only in the return list. And finally, instead of a To: clause we specify the identifying information for the target object as part of the request.

Figure 2 - Representing access with a biderctional interaction

Yet another way to diagram this interaction is shown in figure 3. The interaction is the same as figure 2, but the destination object class has been replaced by the object The System. The System is the system being analysed, which is a high-level object class that contains all the information (including classes, objects, and relationships) in the model.

This is the same as accessing the information from the Animal Care Information high-level object class. Later, during design, interacting with the Animal Care Information object class provides more detail, but during analysis postponing possibly implementation specific details by interacting with The Systemis appropriate.

Figure 3 - Representing access as an interaction with "The System"

Finally, we may show an access interaction with no interaction arrow at all. If the action get diet information for animal is sufficient, no other symbols are necessary. The interaction is implicit.

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Last updated 3 Nov 1994 by Barry Roberts