Computer modelling is to use computer software to represent a real-world problem with a view to better understand the problem. The modeling features of the object-oriented properties include:
- Ability to model complex objects,
- Support of object identity,
- Distinguishing of types and classes, and
- Definition of class hierarchies with inheritance.
Complex objects which are structured in a complex way originate from atomic or already constructed objects by applying certain constructors.
- Tuple, set, bag, list, and array are complex objects.
- The simplest objects are of predefined base types such as integer, character, string, boolean, and real.
The identity of an object is different from its value, and is not equal to pointer (memory address).
- Objects are equal: Objects have the same values.
- Objects are identical: It is the one and the same object.
| Without object identity, the update is difficult to comprehend: |
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Without object identity, the database on the left needs to introduce an artificial key attribute. |
†Object identity can be simulated by means of artificial keys in relational systems; the fundamental difference is that object identity is maintained by the system and thus relieves the programmer of the responsibility.