Optional parameter with UML class diagram

Question

Is there an official syntax for specifying optional parameter of a method in UML class type diagram?

For example, I have a method:

public function abc( $arg = 0) { ... return void; }

How would I indicate that $arg is an optional parameter and its default value?

Answer 1

UML 2.5 has following definition for a parameterlist

• <parameter-list> is a list of Parameters of the Operation in the following format: <parameter-list> ::= <parameter> [‘,’<parameter>]* <parameter> ::= [<direction>] <parameter-name> ‘:’ <type-expression> [‘[‘<multiplicity>’]’] [‘=’ <default>] [‘{‘ <parm-property> [‘,’ <parm-property>]* ‘}’]

where:

• <direction> ::= ‘in’ | ‘out’ | ‘inout’ (defaults to ‘in’ if omitted).
• <parameter-name> is the name of the Parameter.
• <type-expression> is an expression that specifies the type of the Parameter.
• <multiplicity> is the multiplicity of the Parameter. (See MultiplicityElement – sub clause 7.5).
• <default> is an expression that defines the value specification for the default value of the Parameter.
• <parm-property> indicates additional property values that apply to the Parameter.

So you can use

+ abc($arg : Integer = 0)

The type expression is not optional so you can't leave that out, but I guess you can think of a convention where you use something like Unspecified