An abstract class is a rule (an instance of the Rule-Obj-Class class) created to support the definition of rules, including other classes. Such rules can be inherited by subclasses of the abstract class. Rules with a class as a key part (such as properties, activities, flows, data transforms, and so on) can apply to an abstract class.
A class that is not abstract is concrete. Unlike abstract classes, concrete classes can have instances stored in the database. A selection on the Class rule form determines whether a new class is abstract or concrete.
An abstract class can be a child of a higher abstract class.
A selection on the Class form determines whether a class is concrete or abstract.
Concrete classes usually appear near or at the bottom (leaf nodes) of the class hierarchy, but may appear anywhere below the top level.
Abstract Class :- Abstract Class can not be instatiated (It does not create Object to be Stored in DB), In Pega we Use "-"as suffix of Class Name (Naming covention we follow to identify Abstract Class) For ex : Comp-CompFW-
Concrete Class :- The class whihc we can Instantiate (Can be used to create Objects and saved into DB).