I like the idea of a parser using the Google syntax (you don't have to
disable explicit fields BTW - recognzing a term:term syntax should be
doable). The hard problem to crack is what's behind. I explain that in
Hibernate Search in Action, a lot of good search engine do searches in
tiers:
- exact search
- phonetic search
- fuzzy search
- replace ANDs with ORs
I guess you can simulate part of it by boosting exact fields as
opposed to approximation fields in the multi field query parser. This
was not really possible until recently but the
SearchFactory.getAnalyzer(MyEntity.class) makes it much easier.
We should add the Google like feature to the 3.2 list amongst other
higher level query enhancement like spell checking.
Who wants to take the lead? I have always considered grammar and
parser developments awkward for my tastes :)
--
Emmanuel Bernard
http://in.relation.to/Bloggers/Emmanuel | http://blog.emmanuelbernard.com
| http://twitter.com/emmanuelbernard
Hibernate Search in Action (http://is.gd/Dl1)
On Sep 21, 2008, at 05:01, Adam Warski wrote:
Hello,
one feature I find missing from Hibernate Search is a possibility to
easily implement a web search.
A good example is a blog app, where you can search contents of
posts. A post is a simple entity with a "body" field, which is
indexed by Hibernate Search/Lucene.
You then have the normal search box, where the user enters his/hers
query. And now is the problem: what do to with this query?
Solution 1.
Pass it unchanged to the query parser, as is done for example in the
blog example in Seam. But that will in many cases generate
exceptions. For example - when there is an unclosed " or a :. You
can of course catch that exception and return to the user an empty
result list - but that's not what the user excepts.
Solution 2.
Escape any special characters (using QueryParser.escape) and then
pass it safely to query parser - but then the semantics of all
special constructs (like phrases: "...", including/excluding words:
+/-, fuzzy searches: ~ etc) stop to work. That is also not what the
user expects.
My proposed solution.
The best way out, in my opinion, is to create a custom query pre-
parser. This parser would be very "forgiving" in case of any syntax
errors.
I think it would be best to support the query syntax that google
uses (that's what the users are accustomed to):
* standard boolean operators AND, OR
* quotes "..."
* fuzzy/synonym search ~ (but in front of the word, not in the end)
* word inclusion/exclusion: +/-
Some Lucene constructs would be disabled, like boosting (^), field-
search (field_name:), *, ?.
Any special characters in invalid positions would be escaped, for
example an unmatched quote or a + without a word following it. The
parser wouldn't be only a syntax-repairer, but also perform other
operations, like moving the ~ from the beginning of a word to the
end, or (maybe) adding a * to the end of each term.
The implementation shouldn't be too complicated using either ANTLR/
JavaCC or simply regular expressions and a string builder.
Needless to say, this would also be useful in Seam :).
What do you think?
--
Adam
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