I did some refactoring yesterday on the title prefix search suggestion
backend, and added case-insensitive support as an extension.
The prefix search suggestions are currently used in a couple of
less-visible places: the OpenSearch API interface, and the (disabled)
AJAX search option.
The OpenSearch API can be used by various third-party tools, including
the search bar in Firefox -- in fact Wikipedia will be included by
default as a search engine option in Firefox 3.0.
I'm also now using it to power the Wikipedia search backend for Apple's
Dictionary application in Mac OS X 10.5.
We currently have the built-in AJAX search disabled on Wikimedia sites
in part because the UI is a bit unusual, but it'd be great to have more
nicely integrated as a drop-down into various places where you might be
inputting page titles.
The new default backend code is in the PrefixIndex class, which is now
shared between the OpenSearch and AJAX search front-ends. This, like the
previous code, is case-sensitive, using the existing title indexes. I've
also got them now both handling the Special: namespace (which only AJAX
search did previously) and returning results from the start of a
namespace once you've typed as far as "User:" or "Image:" etc.
More excitingly, it's now easy to swap out this backend with an
extension by handling the PrefixSearchBackend hook.
I've made an implementation of this in the TitleKey extension, which
maintains a table with a case-folded index to allow case-insensitive
lookups. This lets you type in for instance "mother ther" and get
results for "Mother Theresa".
In the future we'll probably want to power this backend at Wikimedia
sites from the Lucene search server, which I believe is getting prefix
support re-added in enhanced form.
We might also consider merging the case-insensitive key field directly
into the page table, but the separate table was quicker to deploy, and
will be easier to scrap if/when we change it. :)
-- brion vibber (brion @ wikimedia.org