个人三等功事迹材料:请问这段话怎么翻译谢谢～

A use case is a goal-oriented collaboration between a system and an actor; where an actor is a user adopting a rôle. Such a ‘user’ can be a device or component as well as a person. An agent is anybody or anything adopting a rôle; as opposed to a user doing so. We regard agents and actors as objects, because they exhibit state and behaviour and have identity. If we know the initiator of a collaboration then we can think of a usage dependency as representative of the action. Consider the simple act of buying something illustrated in Figure 13. The ellipse represents an interaction between two agent instances which results in something changing ownership between them
in return for money changing hands in the other direction. This is represented by
an informal post-condition on the action written in the note illustrated. This post- condition only makes sense in terms of the objects it refers to: its parameters. In this case we have identified Thing as a type that must be included in our vocabulary and shown it on our initial drawing. Additionally, we have picked out some of the nouns in the post-condition. This is a very useful technique for inferring the type model from the use cases. We show candidate types in bold, with attributes