Entity Classes (and Objects)
An entity class is the definition of a thing of significance about which the organization wishes to hold (which is to say, collect, maintain, and use) information. This may be a tangible thing like a product or customer, or it may be an intangible thing like a transaction or a role.
In the sample model shown in Figure 2-1, entity classes are represented by rectangles. Organization, Person, Purchase Order, Catalogue Item, and Product are all entity classes.
In the language of object-orientation, an object is an occurrence of an entity. The models described here do not show individual objects (say, purchase order 3245-A). The object-oriented term for entity class is class (as in a “class of objects”), but in this book, ...