Re: help with boolean expression

[Erik Hatcher]

I'm deep into implementing a custom (not generalizable, sorry) query 
parser and am evaluating this very issue now.

Lucene indeed does some funny stuff with boolean operators.  Output the 
toString of your resultant Query's to see the details, or have a look 
at the Bugzilla issue that Morus mentions below.

First some background: BooleanQuery clauses each have their own set of 
required/optional/prohibited attributes.  Putting operators between 
them is awkward in the Lucene sense because the parser has to set each 
clause individually, not in relation to another one.

QueryParser takes the most recent operator and applies it to both the 
clause before and after, and there is no sense of operator precedence 
(such as in a math expression like 1 + 2 * 3).  In the case of A AND B 
OR C, when the AND is encountered, it sets the required attribute for 
both A and B, but then when the OR is encountered it sets the optional 
attribute on B and C, stepping on the previous required flag for B.  
And similarly with A OR B AND C.

I agree that the current behavior is awkward.  Is it worth breaking 
backwards compatibility to correct this with the patch applied?

As for the default operator, it is not coming into play in your 
expression examples because there all clauses have an explicit 
conjunction that sets the flag.  The default operator comes into play 
for an expression like A B AND C and would be used to set the flag on 
the A clause.

        Erik
On Mar 1, 2005, at 9:12 AM, Omar Didi wrote:
I found something kind fo weird about the way lucene interprets 
boolean expressions wihout parenthesis.
when i run the query A AND B OR C, it returns only the documents that 
have A(in other words as if the query was just the term A).
when I run the query A OR B AND C, it returns only the documents that 
have B AND C(as if teh query was just B AND C ). I set the default 
operator in my application to be AND.
can anyone explain this behavior, thanks.

-----Original Message-----
From: Morus Walter [mailto:[EMAIL PROTECTED]
Sent: Monday, February 28, 2005 2:40 AM
To: Lucene Users List
Subject: Re: help with boolean expression
Omar Didi writes:
I have a problem understanding how would lucene iterpret this boolean 
expression : A AND B OR C .
it neither return the same count as when I enter (A AND B) OR C nor A 
AND (B OR C).
if anyone knows how it is interpreted i would be thankful.
thanks
A AND B OR C creates a query that requires A and B. C influcenes the
score, but is neither sufficient nor required for a match.
IMO query parser is broken for queries mixing AND and OR without 
explicit
braces.
My favorite sample is `a AND b OR c AND d' which equals `a AND b AND c 
AND d'
in query parser.

I suggested a patch some time ago, but it's still pending in bugzilla.
http://issues.apache.org/bugzilla/show_bug.cgi?id=25820
Don't know if it's still usable with current sources.
Morus
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