Currently, phpbb URLs look like this:
http://www.phpbb.com/community/viewtopi ... &t=2117269
I've noticed that when I move a topic to another forum, both the original and new links work (although I don't know how that affect watched forums). For example, if I moved this topic to forum 12345, the actual URL would be:
http://www.phpbb.com/community/viewtopi ... &t=2117269 (Notice that URL works even though there's probably no forum 12345.)
but
http://www.phpbb.com/community/viewtopi ... &t=2117269
would still work.
Given that, it seems that topic ID is the only relevant item (and post ID for post links and intra-page links). So couldn't we do something like:
http://www.phpbb.com/community/viewtopi ... -look-like?
(Some of the characters above may need to be replaced or deleted, like the slash after "URLs". For posts, just replace "?f=64&t=..." with "?p=...".)
That way, anything after the topic ID (or post ID or forum ID for forum links) would be ignored (up to any "#p" characters). If the topic title changed to "Pretty URLs", the URL could change to:
http://www.phpbb.com/community/viewtopi ... retty-URLs
with no effect on function or (hopefully) search engines.
Assuming that search engines don't ignore parameters, that seems like it would be easy to do now.
Another idea would be to do something like
Dog Cow's URL changes, but that seems more extensive.
Steve