A popular method is to start with an informal, verbal description of the scenario:
A Customer orders Products or Services.
A Customer is a Person or an Institution.
A Person has a Name consisting of First Name, an optional Middle Name, and a Last Name.
A Person has a Birth Date.
An Institution has a Name.
A Customer has a Customer ID.
A Department receives these Orders.
A Department has a Department ID.
A Department may forward Orders to another Department.
An Order has at least one Position, an Order Date and an Order Number.
Each Position consists of an Amount and a Product or a Service.
A Product has a ProductNo, a Name, and a Description.
A Service has a ProductNo, a Name, a Description, and may have a Duration.
A short grammatical analysis separates these sentences into nouns (Customer, Product, Service, Department, Order) and verbs (order, receive).
In traditional Entity Relationship Modeling all nouns would be modeled as entities, and all verbs would be modeled as relationships. However, there is an ambiguity: The verb "orders" and the noun "Order" relate to the same concept. It remains unclear if the concept should be modeled as an entity or as a relationship.
AOM models both nouns and verbs as assets.
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