The move from NIAM to ORM (Object-Role Modeling) and ORM 2 (called ORM) was motivated by the desire to improve the expressiveness, precision, and usability of the graphical language used for conceptual modelling.
NIAM was the first graphical conceptual modelling language refined by Dr Terry Halpin, but it had some limitations in terms of its expressiveness and ease of use. For example, NIAM was difficult to use for modelling complex relationships.
To address these issues, Dr Halpin developed Object-Role Modeling (ORM), which was first introduced in the 1990s. ORM introduced several new concepts that allowed for a more expressive concepts and relationships in a system being modelled.
ORM was designed with user-friendly symbols and with an aim to be easier to learn.
ORM 2, which was introduced in the early 2000s, extended ORM with new constructs and features, such as derivation rules, subtyping, and role sequences/paths, which further increased the expressiveness and flexibility of the language. ORM 2 is known as ORM.
The impetus for moving from NIAM to ORM and ORM 2 was to provide a more expressive, and user-friendly graphical language for conceptual modelling.