It is pretty common to have relationships that go in two directions. For example, maybe an asset should know which employee is currently holding it. Let’s add that relationship. The new object diagram would look like this:

Figure 20.1  Adding holder relationship

From a design standpoint, you would say that we are adding a pointer from the child (an instance of Asset) back to its parent (the instance of Employee that is holding it).

In Asset.h, add a pointer instance variable to hold on to the holding employee:

#import <Foundation/Foundation.h>
@class Employee;

@interface Asset : NSObject
{
    NSString *label;
    Employee *holder;
    unsigned int resaleValue;
}
@property (strong) NSString *label;
@property (strong) Employee *holder;
@property unsigned int resaleValue;
@end