A URL is a Unified Modeling Language (UML) model element that contains a URL or file path. When you add a URL to you model, it appears in the Model Explorer view and the diagram. In the diagram editor, a comment attachment connects a URL to another diagram element.
You can add a URL or file path to provide access to additional supporting information about a particular diagram element. If appropriate, you can also attach a single URL to multiple diagram elements. You can also add images to your diagrams by adding URLs that reference the image files.
As the following figure illustrates, a URL is displayed as a rectangle with a folded upper-right corner, and a comment attachment is displayed as a dashed line that connects the URL to the diagram element.