: Search we need to translate the Lucene style query into a more traditional
: Boolean query. So this is the opposite of the much discussed Boolean Query
: to Lucene Query conversion.
it should be possible to translate, but like many translations there will
be a small loss of information, specificly: strict boolean queries have no
notion of score, so hte concept of an "optional" clause has no meaning ...
either it's there and you get a match, or it's not and you don't.
You can translate to a query with an equivilent result set, but not one
with equivilent semantic meaning, because the semantics don't apply
(which also means you cannot have a reflexive translation except in
trivial cases)
: Lucene: +a +b -c -d e f
...
: (a AND b NOT c NOT d) OR (a AND b NOT c NOT d AND (e OR f))
...
: (+a +b -c -d)(+a +b -c -d +(e f))
:
: which I think is equivalent but not as concise! But I have not tested this
the first and third are not equivilent .. mainly because they will in fact
score differently. but that's not what you really care about -- what you
realy care about is have you translated the first to the second correctly?
i believe hte answer is "yes" with the caveat that it can be reduced to
just the first clause of hte outermost OR query...
(a AND b NOT c NOT d)
...anything mathcing the second clause of the outermost OR will match
this, making the second clause redundent. you could likewise translate
the lucene query to....
(a AND b NOT c NOT d) OR (a AND b NOT c NOT d AND a AND a AND a AND a)
...the point is they reduce to the same thing.
as a general rule when converting lucene queries to strict boolean
queries: any optional clauses in a BQ containing at least one required
clause can be eliminated, the are irrlevent from a strict matching
standpoint -- they only influence score.
-Hoss
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