The programming interface to ZooKeeper is deliberately simple. With it, however, you can implement higher order operations, such as synchronizations primitives, group membership, ownership, etc.

zookeeper的编程接口特意做的非常简单。在此之上，你可以实现更高层次的操作，如同步原语，组管理，所有权等等。

youdao

We made the decision to allow group members to add others to the group in order to make the product simple, and because it resembles something we all understand: adding one of your contacts to an email thread.

FORBES: Mark Zuckerberg Quits NAMBLA, And Facebook Downplays Privacy Criticisms Over Groups