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From Scott Ganyo <scott.ga...@eTapestry.com>
Subject RE: Problems with prohibited BooleanQueries
Date Thu, 01 Nov 2001 12:40:25 GMT
How difficult would it be to get BooleanQuery to do a standalone NOT, do you
suppose?  That would be very useful in my case.

Scott

> -----Original Message-----
> From: Doug Cutting [mailto:DCutting@grandcentral.com]
> Sent: Wednesday, October 31, 2001 2:36 PM
> To: 'Lucene Users List'
> Subject: RE: Problems with prohibited BooleanQueries
> 
> 
> Lucene does not implement a standalone "NOT" query.  
> (Probably BooleanQuery
> should throw an exception if all clauses are prohibited 
> clauses.)  Negation
> is only implemented with respect to other non-negated clauses.
> 
> So you cannot directly model your query tree as a Lucene 
> query tree.  NOT
> nodes must be incorporated into their parent, a BooleanQuery 
> node, as is
> done in your "directly" case.
> 
> Doug
> 
> > -----Original Message-----
> > From: Anders Nielsen [mailto:anders@visator.dk]
> > Sent: Wednesday, October 31, 2001 10:36 AM
> > To: Lucene Users List
> > Subject: Problems with prohibited BooleanQueries
> > 
> > 
> > Hello,
> > 
> > I have some trouble understanding the semantics of the 
> > BooleanQuery with
> > regards to prohibited clause.
> > 
> > 
> > the method I am using is this:
> > 
> > public final void add(Query query, boolean required, boolean 
> > prohibited)
> > 
> > in the class BooleanQuery.
> > 
> > 
> > I am not using the QueryParser, but instead I build my own 
> > queries from a
> > Tree of search-strings with boolean operators NOT, AND and OR
> > 
> > so a tree might look like this
> > 
> > 	 AND
> > 	/   \
> >     "A"   NOT
> >            |
> >           "B"
> > 
> > and that would mean "documents containing A, but not B". (If 
> > the AND was an
> > OR, the NOT branch would be culled)
> > 
> > 
> > Now my problem is this, when I make a BooleanQuery containing only a
> > prohibited TermQuery and I add that to another BooleanQuery 
> > as a required
> > query, I always get 0 results.
> > 
> > 
> > here's an example of my code:
> > ---------------------------
> >         Term term1 = new Term("name", "jensen");
> >         Term term2 = new Term("name", "barfod");
> > 
> >         BooleanQuery minusQuery = new BooleanQuery();
> >         minusQuery.add(new TermQuery(term2), false, true);
> > 
> >         BooleanQuery q1 = new BooleanQuery();
> >         q1.add(new TermQuery(term1), true, false);
> >         q1.add(minusQuery, false, false);    // not 
> required that the
> > minusQuery is "matched"
> > 
> >         BooleanQuery q2 = new BooleanQuery();
> >         q2.add(new TermQuery(term1), true, false);
> >         q2.add(minusQuery, true, false);     // required that 
> > the minusQuery
> > is "matched"
> > 
> >         BooleanQuery q3 = new BooleanQuery();
> >         q3.add(new TermQuery(term1), true, false);
> >         q3.add(new TermQuery(term2), false, true); // add the 
> > term directly
> > as a prohibited query
> > 
> >         System.out.println("non-required: " + _index.search(q1,
> > null).length());
> >         System.out.println("required    : " + _index.search(q2,
> > null).length());
> > 	  System.out.println("directly    : " + 
> > _index.search(q3, null).length());
> > ---------------------------
> > 
> > this outputs:
> > 
> > non-required: 55
> > required    : 0
> > directly    : 48
> > 
> > 
> > 
> > Regards,
> > Anders Nielsen
> > 
> > 
> > --
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