The indirection from PURLs to less-persistent HTTP URIs is much like the indirection provided by DNS, except that the source and the destination of the redirection are in the same category.
从 PURL 到持久性较底的 HTTP URI，这种的间接性和 DNS 提供的间接性非常相似，只要重定向的来源和目的不在同一类别中即可。