If we're going to separate the concepts of "history" and "paging",
then the term "history" doesn't really apply to incremental feeds.
In an incremental feed, all of the entries are part of the current
state of the feed. We don't go back through history to find the
present--we go to different pages of the present. In a non-
incrememental feed also, we may have multiple pages of current
entries (eg. the top 100 DVDs in chunks of 10), or we may have just
one. We also may preserve historical data (eg. the top 10 songs last
week, the week before, etc.)
So what we end up with might looks like this:
Any feed, whether incremental or not, MAY contain something like this
(names chosen somewhat arbitrarily, with an eye toward avoiding
excess conceptual baggage):
page-a - the URI of one end of a chain of documents representing one
state of a feed resource (eg. the current state of an incremental
feed)--it doesn't really matter which end it is
page-b - the other end of the chain of documents
page++ - the next farther page from page-a
page-- - the next closer page to page-a
Neither "page-a" nor "page-b" is necessarily fixed--the entire
contents of the chain may shuffle around, be added to, be deleted
from, etc., in the case of something like search results.
A non-incremental feed MAY also contain something like this (history
is temporal, so we can use temporally loaded terminology):
history-1 - a document containing a representation of one of the ends
of or the entire temporally first historical state of the feed resource
history-n - a document containing a representation of one of the ends
of or the entire temporally last (perhaps current and still changing)
historical state of the feed resource
history++ - one of the ends or ... of the the next more recent
historical state... (moves toward history-n)
history-- - one of the ends ... of the next less recent historical
state... (moves toward history-1)
If you want to catch up on an incremental feed to which you're
subscribed, or want to get the last month of an incremental feed to
which you are newly subscribed, you look for "page++" or "page--" and
follow whichever one the subscription document (which can only have
one, since it's one of the ends) contains till you've got everything
you want.
If you start in the middle, you don't know which direction you're
going...but since the ordering of the chain isn't defined, it's like
the Cheshire cat says--it doesn't matter which direction you go if
you don't know where you want to end up...or something like that.
Perhaps convention could dictate that "page-a" be where the publisher
subjectively thinks that a newcomer to the feed would be most likely
to want to start reading. It wouldn't always be correct, but so what?
