I like to think of it like this:
Each doc is going to get a score -- if the score is positive the doc
will be a hit, if the score is 0 the doc will not be a hit.
If a boolean clause is Occur.Must and it is not found, the score will be
dropped to 0 no matter what (if found, the score is obviously
increased). If a boolean clause is Occur.Must_Not and is found then the
score will be dropped to 0 no matter what.
If the boolean query is Occur.Should and it is found a positive number
is added to the score...if it is not found, nothing is added to the score.
Now you see why it says: "Use this operator for clauses that /should/
appear in the matching documents. For a BooleanQuery with two |SHOULD|
subqueries, at least one of the clauses must appear in the matching
documents."
To get a positive score and make a hit, one of the Occur.Should clauses
needs to be found to increase the score above 0.
- Mark
Peter Bloem wrote:
I'm constructing a search with some required terms and some optional
terms in in the query. According to some earlier posts that looks like
"+(A B) C D E" in query syntax for required terms A and B and optional
terms C D and E. In other words, Lucene considers all documents that
have both A and B, and ranks them higher if they also have C D or E.
I'm wondering how this translates to a BooleanQuery. I know I should
use BooleanClause.Occur.MUST for A and B, and I guess I should use
BooleanQuery.Occur.SHOULD for C, D and E. However the javadocs for
BooleanClause.Occur.SHOULD states:
"Use this operator for clauses that /should/ appear in the matching
documents. For a BooleanQuery with two |SHOULD| subqueries, at least
one of the clauses must appear in the matching documents."
Does this last sentence actually mean that a query with _just_ two
SHOULD clauses (ie. only SHOULD clauses) must contain one of the
clauses, or will the BooleanQuery described above actually constrain
the search results to (A AND B) AND (B OR C OR D)? If so, what should
I use instead?
thank you,
Peter
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