Object models are the models that describe the system in terms of object classes and their associations.
- An object class is an abstraction over a set of objects with common attributes and the services provided by each object.
- Natural ways of reflecting the real-world entities manipulated by the system.
- More abstract entities are more difficult to model using this approach.
- Object classes reflecting domain entities are reusable across systems.
Various object models may be produced as:
1 Inheritance Model
- Organizes the domain object classes into a hierarchy.
- Classes at the top of the hierarchy reflect the common features of all classes.
- Object classes inherit their attributes and services from one or more super-classes.
- Class hierarchy design can be a difficult process if duplication in different branches is to be avoided.
Fig: Library class hierarchy as Inheritance Model
2 Aggregation Model
- An aggregation model shows how classes that are collections are composed of other classes.
- Aggregation models are similar to the part-of relationship in semantic data models.
Fig: Demonstration of object aggregation model
3 Interaction Model
- The interaction model shows the interactions between objects to produce some particular system behavior that is specified as a use-case.
- Sequence diagrams (or collaboration diagrams) in the UML are used to model interaction between objects.
Fig: Sequence diagram as interaction model
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