Core modelling concepts in object-oriented conceptual modelling

Many concepts in object-oriented conceptual modelling have complex semantics that are unfortunately not precisely defined. This paper demonstrates that, with a few simple and formally defined concepts, one can define more complex concepts (such as, for example, aggregation) in a precise and formal way. The core concepts offer the possibility of layering modelling concepts: a particular pattern of simple lower-level concepts can be used to represent a single high-level concept. The advantage is that the high-level concept is defined in terms of the lower-level concepts. Because of their simplicity, the lower-level concepts are much easier to define formally. The high-level concept benefits from this formal definition: its own formal definition can be inferred from the formal definition of its constituent lower-level concepts. This layered approach can also be followed on a project-by-project basis by defining high-level concepts that are only applicable in the context of one particular project.