Question

Explain the backgrounds and the rationale for the following modelling advice: When you are in doubt whether you should model a relationship as an association or an aggregation, model it as an association.

Answer 1

Explain the background and the rationale for the following modeling advice : When you are in doubt whether you should model a relationship as an association or an aggregation, model it as an association --

• The association -- association represent binary relationship between two objects that describe an activity.
• for example - A doctor can be associated with multiple patients.
• To represent relationship between componants or classes, it uses line segment.
• By Modeling it as an Association, structural relationship that represent object which can be associated with another objects in the sytsem.
• The constraints of association relationship are --
• Implicit - the implicit relationship is based on concept not on manifest.
• Ordered - This constriants specify that set of object at one end of assoiation is in specific way.
• Changeable - This connection between various object in system can be added, modified and removed.as requirements.
• Frozen - When link is inserted between two objects , at that time it can not be modified while frozen constraint is active on given link.
• addOnly - It specify new connection can be added from object which is situated at other end association.

Aggregation - This is used to model compositional relationship between model elements. for example - a library contains books and computer composed of number of devices.

• The aggregation is based on main classes that are dependent on sub classes. in this, sub class can exists without main class but main class can not exists without subclass.
• The aggregation relationship is represented by "has" relationship. for example - List of phone numbers.
• To represent relationship between objects, it use diamond shape structure.