Type extensions, which enable you to extend an existing type easily without the additional overhead work of creating a new derived type.

型别扩充，可让您轻松扩充现有型别，而不需要额外建立新的衍生型别。

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When you add a lifeline to an interaction (sequence diagram), its type is stored in the root model, unless you have created the lifeline from an existing type.

除非您是基于现有类型创建了生命线，否则向交互（序列图）添加生命线时，其类型将存储在根模型中。

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The second piece of evidence pointing to is the eccentric orbit of an existing planet around the star, which is in an orbit not normally expected in this type of system.

FORBES: Astronomers Discover A Star That May Have Destroyed Its Own Planet

Apple's challenge is that getting people to buy an iPod, a new type of device, is easier than getting them to switch loyalties in an existing product category.

ECONOMIST: The iPod has turned Apple into a superbrand

No one now knows how easy it would be to turbo-charge an existing human pathogen, or take one that infects another type of animal and assist its passage over the species barrier.

ECONOMIST: Synthetic biology