Identifiers like URIs are persistent, but the representations it provides you are not persistent over time.
So, if I provide a URI that means "a list of links to various resources with interesting data", those linked URIs can be bookmarked (they're persistent), but the original URI has every right to change the links later on if it thinks there are more relevant ones (e.g. newer, more relevant, etc.). Think of how a news site's main page changes with "Top News Stories", for example. That doesn't mean the older URIs it pointed yesterday to are necessarily bad.
So, if I provide a URI that means "a list of links to various resources with interesting data", those linked URIs can be bookmarked (they're persistent), but the original URI has every right to change the links later on if it thinks there are more relevant ones (e.g. newer, more relevant, etc.). Think of how a news site's main page changes with "Top News Stories", for example. That doesn't mean the older URIs it pointed yesterday to are necessarily bad.
For a RESTful machine-to-machine interface, this HATEOS approach is arguably one of the more effective ways to do extensibility and versioning: http://www.mnot.net/blog/2011/10/25/web_api_versioning_smack...