Although UML is normally is often used for object-orientated design, it can be worth it to create UML for other applications too. Pictured below is a ‘use case’ diagram. Use case diagrams are representations of a user’s interactions with the system. The system in this diagram is the miXXers social network. The green bubbles represent use cases, things the user could do within miXXers. The lines link actors (in this case a generic user of miXXerS) and the use cases they have access to. Lines can also occur between use cases  in order to indicate relationships between them. An extend for example, is used to indicate a use case conditionally adds steps to another use case. Although not used here, there are many other types of UML diagrams which could be used to model structures, relationships and communications.

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