The realation icon which is on the use case is disabled?why?

the realation icon which is on the use case is disabled?why?

I’m not fully sure what you mean with “relation icon”; I assume you’re referring to the small arrow in the lower right corner which indicates that you have set up a sub-diagram?

Either way, those icons are model indicators. They’re used to show that there’s something extra “attached” to your model element. From the master & auxiliary view, sub-diagrams, an added description right down to an attached file.

Check the “view” tab, you’ll find an option called “Model indicator”; this controls whether these indicators are visible or not. Another way to do this is to right click on your diagram, find the “Presentation options” section in the pop-up menu, and select “Always Show Model Element Indicators”.

Hope this helped!