Are field types in class diagram obligatory?

Question

When specifying class fields in class diagram you can provide their types, e.g.:

- name : string
- age : int

Same with methods:

+ getName() : string

You can also omit the type if the method doesn't have/return one:

+ ClassName()   // constructor
+ performCleanup()   // returns void

1. But what if the diagram only presents some example fields (i.e. presenting the design pattern idea) and the concrete type is unimportant? Do I pick any type at random for the field or should I omit the type?

   • sampleField1 : int // arbitrary type
   • sampleField2 // no type specified

---

2. Also, is providing field types obligatory in general? Should I always do it?

Answer 1

TL;DR You can omit the type and it is not obligatory, sometimes you even don't know the exact types or you just don't care, e.g. in uml-diagrams.org: Library Domain Model, UML Class Diagram Example

---

UML 2.4.1 Infrastructure specification says:

...10.2.5 Property

...A property is a typed element that represents an attribute of a class...

...10.1.5 TypedElement

...A typed element is a kind of named element that represents elements with types...

...Elements with types are instances of TypedElement. A typed element may optionally have no type...

See also:

• What is the difference between a domain class diagram and a design class diagram?