Perfect property: Locating a table entry requires o (1) time-that is, at most, one string comparison is required to perform keyword recognition within the static search set.

perfect property：查找时间复杂度为o(1)的表条目—就是说，至多需要一个字符串比较执行静态搜索集中的关键字识别。

youdao

All the search engines follow these robot directives, which, while not a perfect security solution, limit the entry points used by the bots and spiders that index the Web.

FORBES: Google Me Not