@startuml
'figure 1: abc diagram'
skinparam monochrome true
skinparam handwritten false
skinparam shadowing false
hide class circle
skinparam classAttributeIconSize 0

class "abc.ABC" as abc {}

abstract class BaseClass {
+ {abstract} a_method()
}

class ConcreteClass_1 {
+ a_method()
}

class ConcreteClass_2 {
+ a_method()
}

abc <|-- BaseClass
BaseClass <|-- ConcreteClass_1
BaseClass <|-- ConcreteClass_2


@enduml
