Nice write up, Stas!

I worry that with the "best possible query" will be confusing or undesirable because the ranking will be lousy, as you suggest. You can test it and see—in RelForge you can compare the namespace-specific scoring function and a proposed generic scoring function for a sample of queries in a particular namespace and see how much it churns the top results.

For the "garden of forking queries" (most excellent poetic naming of options!!), there is a straightforward though somewhat tedious way of merging rankings. You can use an empirical distribution function on a largish sample of scores for each ranking function, and then normalize them to a range of 0.0-1.0. (RelForge even has a tool to generate a more tractable and reasonably accurate piecewise linear approximation given empirical distribution data.) Effectively, you turn all scores into percentiles, and assume those are comparable. It's ugly, but if that's the only thing holding you back from that option, it's doable. It is tedious and a bit brittle, though, because if the scoring function for any component changes, you need to regenerate its EDF function—though that task could be automated to some degree if it comes up regularly.

—Trey

Trey Jones

Sr. Software Engineer, Search Platform
Wikimedia Foundation

On Wed, May 30, 2018 at 8:26 PM, Stas Malyshev <smalyshev@wikimedia.org> wrote:

Hi!

While working on fulltext search for Lexemes, I have encountered a
question which I think needs to be discussed and resolved. The question
is how fulltext search should be working when dealing with different
content models and what search should do by default and in specialized
cases.

The main challenge in Wikidata is that we are dealing with substantially
different content models - articles, Items (including Properties,
because while being formally different type, they are similar enough to
Items for search to ignore the difference) and Lexemes organize their
data in a different way, and should be searched using different
specialized queries. This is currently unique for Wikidata, but SDC
might eventually have the same challenge to deal with. I've described
challenges and questions there are here in more detail:

https://www.wikidata.org/wiki/User:Smalyshev_(WMF)/Wikidata_search#Fulltext_search

I'd like to first hear some feedback about what are the expectations
about the combined search are - what is expected to work, how it is
expected to work, what are the defaults, what are the use cases for
these. I have outlined some solutions that were proposed on wiki, if you
have any comments please feel welcome to respond either here or on wiki.

TLDR version of it is that doing search on different data models is
hard, and we would need to sacrifice something to make it work. We need
to figure out and decide which of these sacrifices are acceptable and
what is enabled/disabled by default.

Thanks,
--
Stas Malyshev
smalyshev@wikimedia.org

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