Plantuml class diagram with multiple children: Any way to bifurcate the arrow?

Question

My attempt:

Animal <|-- Cat
Animal <|-- Dog

Result:

  ┌────────┐
  │ Animal │
  └────────┘
   Δ      Δ
   │      │
┌──┴──┐┌──┴──┐
│ Cat ││ Dog │
└─────┘└─────┘

That is not how a class diagram is supposed to look like.

This is:

  ┌────────┐
  │ Animal │
  └────────┘
      Δ
   ┌──┴───┐
┌──┴──┐┌──┴──┐
│ Cat ││ Dog │
└─────┘└─────┘

As suggested, I asked if this is possible on the PlantUML forum.

I think the class diagram should / can look like this as the `cat` and `dog` are independently derived from `animal`. From where do you get that the arrows should be joined first? — albert, Sep 06 '18 at 11:52
@albert That's how I [learnt it](https://martinfowler.com/books/uml.html). The first illustration in the [wikipedia article](https://en.wikipedia.org/wiki/Class_diagram) is also like that. — user2394284, Sep 06 '18 at 11:58
I don't think it is possible in plantuml, maybe best to ask at http://forum.plantuml.net/questions as well. — albert, Sep 06 '18 at 12:51

score 5 · Accepted Answer · edited Nov 22 '18 at 10:00

5

You can do something like this:

@startuml
class Animal
together {
  class Dog
  class Cat
}
Animal <|-- Cat
Dog -- (Animal, Cat)
@enduml

result

edited Nov 22 '18 at 10:00

albert

8,285
3
19
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answered Nov 21 '18 at 21:45

Petr Prouza

76
1
4

Depending on the style the black dot looks bad but I can't find any skinparam nor CSS style to change the color or existence of that dot. Also, [it seems](https://forum.plantuml.net/7125/inside-namespace-classes-defined-together-recognized-outside) that `together` can't be used inside namespaces but works fine with packages. – mxmlnkn Jul 07 '21 at 21:19

score 5 · Answer 2 · answered Jul 23 '20 at 21:14

There's skinparam groupInheritance 2 which will serve your purpose, although it doesn't work with skinparam linetype ortho as one might expect. Alas, GraphViz is the rendering engine, so that has limitations.

@startuml
skinparam style strictuml
hide empty members
skinparam groupInheritance 2
class Animal
class Cat extends Animal
class Dog extends Animal
@enduml

score 2 · Answer 3 · edited Jul 23 '20 at 21:19

An interesting thing to do in plantUML but "this is not how class diagram is supposed to look like" is not correct (to my knowledge, at least).

The notation is clear for inheritance/generalization but whether you join the lines before the arrow or have separate lines with separate arrows is a matter of visual preference/making it easier to understand:

Try to sketch the image on top of that wiki you linked with distinct arrow from each child to it's parent, it will be much more messy
Scroll down a bit on wiki to https://en.wikipedia.org/wiki/Class_diagram#Generalization/Inheritance

Plantuml class diagram with multiple children: Any way to bifurcate the arrow?

3 Answers3

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