Marvin Humphrey wrote on 8/28/12 12:56 AM:
> On Mon, Aug 27, 2012 at 8:09 PM, Peter Karman <[email protected]> wrote:
>> * I am intrigued by MatchEngine. Would it make what I'm trying to do above
>> any easier?
>
> While it wouldn't diminish the raw volume of code, I think it would make
> things easier to understand.
>
> * It allows us to eliminate Compiler.
> * People creating custom query subclasses would have the option of writing
> only a Query/Matcher pair rather than a Query/weighted-Query/Matcher trio.
I like both those things.
>
> Here's a rapid prototype for TFIDFMatchEngine:
>
> package Lucy::TFIDF::TFIDFMatchEngine;
> use base qw( Lucy::Search::MatchEngine );
>
> sub weight_query {
> my ($self, %args) = @_;
> my ($query, $searcher) = @args{qw( query searcher )};
> my $query_class = ref($query);
> if ($query_class eq 'Lucy::Search::TermQuery') {
> return Lucy::TFIDF::TFIDFTermQuery->new(
> parent => $query,
> searcher => $searcher,
> );
> }
> elsif ($query_class eq 'Lucy::Search::PhraseQuery') {
> return Lucy::TFIDF::TFIDFPhraseQuery->new(
> parent => $query,
> searcher => $searcher,
> );
> }
> ... # ...and so on for all core Query classes.
> else {
> # Unknown Query class, so fall back to delegating weighting to the
> # Query itself. (Since TFIDFMatchEngine doesn't know how to
> # produce a weighted query for this Query class, we have to hope
> # that this is a custom Query class written with TFIDFMatchEngine
> # as a target and that it knows how to create a weighted query
> # appropriate for TFIDFMatchEngine.)
> return $query->make_weighted_query(
> searcher => $searcher
> match_engine => $self,
> );
> }
> }
>
ok, that all makes sense to me. Could we make the Lucy::TFIDF::* classes public
so that (as in my case) they could be extended, rather than just replaced?
>> I started thinking of Compiler as WeightedQuery, and its relationship to
>> Query
>> as similar to the relationship between Doc and HitDoc. I imagined code like:
>>
>> my $query = $queryparser->parse('foo'); # $query isa Query
>> $query->apply_weight(searcher => $searcher); # $query isa WeightedQuery
>> if (!$query->weighted) {
>> die "can't score a search without weighting the query";
>> }
>
> FWIW, mutating Query objects is what Lucene originally did, back in
> version 1.3 IIRC. :P
>
man. I am so old and in the weigh.
> Here's something very similar:
>
> my $query = $queryparser->parse('foo');
> my $weighted_query = $match_engine->weight_query(
> searcher => $searcher,
> query => $query
> );
> if (!$weighted_query->weighted) {
> die "can't score a search without weighting the query";
> }
>
> The difference is that while your sample code mutates $query, this version
> uses a factory method which generates a new $weighted_query and leaves the
> original $query untouched.
>
> There are a lot of reasons that we want to avoid mutating the original Query
> object. For starters, we have long wanted to sever the connection between our
> Query classes and TFIDF (or any other scoring model) -- but if they must hold
> weighting information, they have to know about the scoring model.
>
+1 I get why the mutation is to be avoided.
--
Peter Karman . http://peknet.com/ . [email protected]
