A model is the attempt to describe as well as possible, and as detailed as necessary, the reality of a certain domain. A model consists of various parts that we are now going to inspect in detail.
An entity is an object that is uniquely identifiable by a combination of its attributes and has a well-defined lifespan. It starts to exist at a well-defined moment in time, it can also be destroyed or terminated in such a well-defined moment in time. Often, the entity contains an ID or key attribute, which is used to uniquely identify it.
Two entities of the same type and having the same identifier are considered to be the same entity.
In a model, we call those types of objects entity, whose identity and life cycle is of importance. ...