Ontology snapshots for log:semantics

Using log:semantics, I can describe a rule to make inferences from an ontology at a URL (such as
http://www.w3.org/2000/10/swap/grammar/n3.n3).  But someone may change that document, so the rule's meaning
could change.
This is a general problem of referring to a document at a URL which may change.

Is there a standard way to refer to a "snapshot" of a document at a URL *at a specific time*?
(For example, archive.org uses
http://web.archive.org/web/20070208203121/http://www.w3.org/2000/10/swap/grammar/n3.n3 )
This way, if someone is using a caching proxy like squid, when they use the rule
with log:semantics they fetch the *same* document so that the rule can have the intended meaning
and returns the same results.

- Jeff