Entities and Classes
An Entity Type is a named, structured data type whose named components are called attributes, properties or fields.
A Class extends an abstract data type by allowing multiple instances. A class extends an Entity Type by defining a set of methods or operations that can be applied to any class instance.
- Instances of a Class are called objects.
- Class methods may update values
- The value of an Entity or Class Instance is specified by assigning a value to each of its component attributes or data members.
- Each attribute has a data type which defines (and is defined by) its ‘Attribute Domain’ (set of legal values).
- An Entity Domain is [a subset of] the set-theoretic direct or Cartesian product of its attribute domains.