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https://issues.apache.org/jira/browse/LUCENE-2458?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12866363#action_12866363
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Hoss Man commented on LUCENE-2458:
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bq. a Boolean Query formed with the default operator.
That seems like equally bad default behavior -- lots of existing TokenFilters
produce chains of tokens for situations where the user creating the query
string clearly intended to be searching for a single "word" and has no idea
that as an implementation detail multiple tokens were produced under the covers
(ie: WordDelimiterFilter, Ngrams, etc...)
I haven't thought this through very well, but perhaps this is an area where
(the new) Token Attributes could be used to instruct QueryParser as to the
intent behind a stream of multiple tokens? A new Attribute could be used on
each token to convey when that token should be combined with teh previous
token, and in what way: as a phrase, as a conjunction or as a disjunction.
(this could still be orthogonal to the position, which would indicate slop/span
type information like it does currently)
Stock Analysys components that produce multiple tokens could be modified to add
this attribute fairly easily (it should be a relatively static value for any
component that currently "splits" tokens) and QueryParser could have an option
controlling what to do if it encounters a token w/o this attribute (perhaps
even two options: one for quoted input chunks and one for unquoted input
chunks).
that way the default could still work in a back compatible way, but people
using languages that don't use whitespace separation *and* are using older (or
custom) analyzers that don't know about this attribute could set a simple query
parser property to force this behavior.
would that make sense? (asks the man who only vaguely understands Token
Attributes at this point)
> queryparser shouldn't generate phrasequeries based on term count
> ----------------------------------------------------------------
>
> Key: LUCENE-2458
> URL: https://issues.apache.org/jira/browse/LUCENE-2458
> Project: Lucene - Java
> Issue Type: Bug
> Components: QueryParser
> Reporter: Robert Muir
> Priority: Critical
>
> The current method in the queryparser to generate phrasequeries is wrong:
> The Query Syntax documentation
> (http://lucene.apache.org/java/3_0_1/queryparsersyntax.html) states:
> {noformat}
> A Phrase is a group of words surrounded by double quotes such as "hello
> dolly".
> {noformat}
> But as we know, this isn't actually true.
> Instead the terms are first divided on whitespace, then the analyzer term
> count is used as some sort of "heuristic" to determine if its a phrase query
> or not.
> This assumption is a disaster for languages that don't use whitespace
> separation: CJK, compounding European languages like German, Finnish, etc. It
> also
> makes it difficult for people to use n-gram analysis techniques. In these
> cases you get bad relevance (MAP improves nearly *10x* if you use a
> PositionFilter at query-time to "turn this off" for chinese).
> For even english, this undocumented behavior is bad. Perhaps in some cases
> its being abused as some heuristic to "second guess" the tokenizer and piece
> back things it shouldn't have split, but for large collections, doing things
> like generating phrasequeries because StandardTokenizer split a compound on a
> dash can cause serious performance problems. Instead people should analyze
> their text with the appropriate methods, and QueryParser should only generate
> phrase queries when the syntax asks for one.
> The PositionFilter in contrib can be seen as a workaround, but its pretty
> obscure and people are not familiar with it. The result is we have bad
> out-of-box behavior for many languages, and bad performance for others on
> some inputs.
> I propose instead that we change the grammar to actually look for double
> quotes to determine when to generate a phrase query, consistent with the
> documentation.
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