2.7. UML Relationship

Important

• Arrow with empty triangle (but on picture is filled)

• <|-- - Inheritance

• *-- - Composition

• o-- - Aggregation

• --> - Association

• -- - Link (Solid)

• ..> - Dependency

• ..|> - Realization

• .. - Link (Dashed)

2.7.1. Inheritance

✘

>>> class Vehicle:
...     def engine_start(self): pass
...     def engine_stop(self): pass
>>>
>>>
>>> class Car(Vehicle):
...     pass
>>>
>>> class Truck(Vehicle):
...     pass
>>>
>>> class Motorcycle(Vehicle):
...     pass

```mermaid
classDiagram
    Vehicle <|-- Car
    Vehicle <|-- Truck
    Vehicle <|-- Motorcycle

    class Vehicle {
        engine_start()
        engine_stop()
    }
```

2.7.2. Linear Inheritance

✘

>>> class Vehicle:
...     def engine_start(self): pass
...     def engine_stop(self): pass
>>>
>>> class VehicleWithWindows(Vehicle):
...     def window_open(self): pass
...     def window_close(self): pass
>>>
>>>
>>> class Car(VehicleWithWindows):
...     pass
>>>
>>> class Truck(VehicleWithWindows):
...     pass
>>>
>>> class Motorcycle(Vehicle):
...     pass

```mermaid
classDiagram
    Vehicle <|-- Motorcycle
    Vehicle <|-- VehicleWithWindows
    VehicleWithWindows <|-- Car
    VehicleWithWindows <|-- Truck

    class Vehicle {
        engine_start()
        engine_stop()
    }

    class VehicleWithWindows {
        window_open()
        window_close()
    }
```

2.7.3. Multiple Inheritance

• Also know as Mixin Classes

✘

>>> class Vehicle:
...     pass
>>>
>>> class HasEngine:
...     def engine_start(self): pass
...     def engine_stop(self): pass
>>>
>>> class HasWindows:
...     def window_open(self): pass
...     def window_close(self): pass
>>>
>>> class Car(Vehicle, HasEngine, HasWindows):
...     pass
>>>
>>> class Truck(Vehicle, HasEngine, HasWindows):
...     pass
>>>
>>> class Motorcycle(Vehicle, HasEngine):
...     pass

```mermaid
classDiagram
    HasWindows --* Car
    HasWindows --* Truck

    Vehicle --* Car
    Vehicle --* Truck
    Vehicle --* Motorcycle

    class Vehicle {
        engine_start()
        engine_stop()
    }

    class HasWindows {
        window_open()
        window_close()
    }
```

2.7.4. Composition

✘

>>> class Vehicle:
...     pass
>>>
>>> class Engine:
...     def engine_start(self): pass
...     def engine_stop(self): pass
>>>
>>> class Windows:
...     def window_open(self): pass
...     def window_close(self): pass
>>>
>>>
>>> class Car(Vehicle):
...     engine: Engine
...     window: Windows
>>>
>>> class Truck(Vehicle):
...     engine: Engine
...     window: Windows
>>>
>>> class Motorcycle(Vehicle):
...     engine: Engine

```mermaid
classDiagram

    class Engine {
        engine_start()
        engine_stop()
    }

    class Car {
        engine: Engine
    }

    class Truck {
        engine: Engine
    }

    class Motorcycle {
        engine: Engine
    }
```

2.7.5. Aggregation

✘

>>> class Group:
...     gid: int
...     name: str
>>>
>>>
>>> class User:
...     firstname: str
...     lastname: str
...     groups: list[Group]

✘

>>> class Vehicle:
...     pass
>>>
>>> class Part:
...     pass
>>>
>>> class Engine(Part):
...     def engine_start(self): pass
...     def engine_stop(self): pass
>>>
>>> class Windows(Part):
...     def window_open(self): pass
...     def window_close(self): pass
>>>
>>>
>>> class Car(Vehicle):
...     parts: list[Part] = [Engine, Windows]
>>>
>>> class Truck(Vehicle):
...     parts: list[Part] = [Engine, Windows]
>>>
>>> class Motorcycle(Vehicle):
...     parts: list[Part] = [Engine]

```mermaid
classDiagram

    class User {
        firstname: str
        lastname: str
        groups: list[Group]
    }

    class Group {
        gid: int
        name: str
    }

    User *--|> Group
```

2.7.6. Dependency

• Somewhere in User class you are using Spaceship class

✘

>>> class Group:
...     name: str
>>>
>>>
>>> class User:
...     firstname: str
...     lastname: str
...
...     def join(group: Group):
...         pass

```mermaid
classDiagram
    User ..> Group

    class User {
        firstname: str
        lastname: str
        join(group: Group)
    }

    class Group {
        name: str
    }
```

2.7.7. Cardinality

• 0 - Exactly 0

• 0..1 - Zero or one

• 0..n - Zero to n (where n > 1)

• 0..* - Zero or more

• 1 - Only one

• 1..n - One to n (where n > 1)

• 1..* - One or more

• * - Many

• n..n - {where n>1}