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In UML class diagram notation, how do I denote a top-level function that doesn't have any encapsulating class or other structure?

e.g. I have a function used for retrieving data from a URL. Since it is a function (in the math sense) of only its parameters and a shared global state, the function is not put in a class but left as a top-level method.

Now though, I need to create a UML diagram for a program using it, and I can't find anything about how to denote a top-level function. How do I do this?

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  • You can model it as static method of a special class called e.g. global
    – xmojmr
    Nov 3, 2015 at 6:42
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    The answers below are good. However, rather than call the class or stereotype "global" I think "StandaloneFunction" is better as it is very explicit to your intent. With that said, IMO even better would be to put the "top-level" functions in a well named namespace which allows for organizing of the functions and then gives you a class to put them in. Thus, putting the function in a namespace called UrlUtilities is far superior to just having this be a "top-level" function. But then again, at this point you may as well put it in a UrlUtilities class as a static method which is the best option.
    – Dunk
    Nov 9, 2015 at 21:56

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Create a stereotype that you can attach to the "class" classifier, e.g., <<global function>>. You can then create a single stereotyped "class" for each global function containing one fully specified static operation.

The stereotype I propose tells the person reading the diagram to interpret the classifier as a function. The rectangle (with the stereotype) on a given diagram would represent a single function, while its dependencies represent the dependencies of that single function.

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  • I am having a difficult time seeing how your answer is different than Bart's...
    – Adam Zuckerman
    Nov 9, 2015 at 23:30
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    @AdamZuckerman - Bart creates a single class called "global" that aggregates all global functions, making it difficult to know which global function and dependencies apply in the give context. The stereotype I propose tells the person reading the diagram to interpret the class as a function instead. A class rectangle (with the stereotype) would represent a single function, while it's dependencies represent the dependencies of that single function.
    – Doug Knesek
    Nov 10, 2015 at 0:22
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The UML language does not support the notion of stand-alone functions. Within UML, all functions must be part of a class.

As a work-around, you could model your stand-alone functions as static members of a class they are closely related to. If there is no such class, then you could model those functions as being part of a dummy class, like the global class mentioned by @xmojmr in the comments.

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