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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#include "bm25_feature.h"
#include "utils.h"
#include <vespa/searchlib/fef/featurenamebuilder.h>
#include <vespa/searchlib/fef/itermdata.h>
#include <vespa/searchlib/fef/itermfielddata.h>
#include <vespa/searchlib/fef/objectstore.h>
#include <vespa/searchlib/fef/properties.h>
#include <vespa/vespalib/util/stash.h>
#include <cmath>
#include <stdexcept>
#include <vespa/log/log.h>
LOG_SETUP(".features.bm25_feature");
namespace search::features {
using fef::AnyWrapper;
using fef::Blueprint;
using fef::FeatureExecutor;
using fef::FeatureNameBuilder;
using fef::FieldInfo;
using fef::FieldType;
using fef::ITermData;
using fef::ITermFieldData;
using fef::MatchDataDetails;
using fef::objectstore::as_value;
using vespalib::Trinary;
namespace {
double
get_inverse_document_frequency(const ITermFieldData& term_field,
const fef::IQueryEnvironment& env,
const ITermData& term)
{
double fallback = Bm25Executor::calculate_inverse_document_frequency(term_field.get_matching_doc_count(),
term_field.get_total_doc_count());
return util::lookupSignificance(env, term, fallback);
}
}
Bm25Executor::Bm25Executor(const fef::FieldInfo& field,
const fef::IQueryEnvironment& env,
double avg_field_length,
double k1_param,
double b_param)
: FeatureExecutor(),
_terms(),
_avg_field_length(avg_field_length),
_k1_mul_b(k1_param * b_param),
_k1_mul_one_minus_b(k1_param * (1 - b_param))
{
for (size_t i = 0; i < env.getNumTerms(); ++i) {
const ITermData* term = env.getTerm(i);
for (size_t j = 0; j < term->numFields(); ++j) {
const ITermFieldData& term_field = term->field(j);
if (field.id() == term_field.getFieldId()) {
_terms.emplace_back(term_field.getHandle(MatchDataDetails::Interleaved),
get_inverse_document_frequency(term_field, env, *term),
k1_param);
}
}
}
}
double
Bm25Executor::calculate_inverse_document_frequency(uint32_t matching_doc_count, uint32_t total_doc_count)
{
return std::log(1 + (static_cast<double>(total_doc_count - matching_doc_count + 0.5) /
static_cast<double>(matching_doc_count + 0.5)));
}
void
Bm25Executor::handle_bind_match_data(const fef::MatchData& match_data)
{
for (auto& term : _terms) {
term.tfmd = match_data.resolveTermField(term.handle);
}
}
void
Bm25Executor::execute(uint32_t doc_id)
{
feature_t score = 0;
for (const auto& term : _terms) {
if (term.tfmd->getDocId() == doc_id) {
feature_t num_occs = term.tfmd->getNumOccs();
feature_t norm_field_length = ((feature_t)term.tfmd->getFieldLength()) / _avg_field_length;
feature_t numerator = num_occs * term.idf_mul_k1_plus_one;
feature_t denominator = num_occs + (_k1_mul_one_minus_b + _k1_mul_b * norm_field_length);
score += numerator / denominator;
}
}
outputs().set_number(0, score);
}
Trinary
Bm25Blueprint::lookup_param(const fef::Properties& props, const vespalib::string& param, double& result) const
{
vespalib::string key = getBaseName() + "(" + _field->name() + ")." + param;
auto value = props.lookup(key);
if (value.found()) {
try {
result = std::stod(value.get());
return Trinary::True;
} catch (const std::invalid_argument& ex) {
LOG(warning, "Not able to convert rank property '%s': '%s' to a double value",
key.c_str(), value.get().c_str());
return Trinary::Undefined;
}
}
return Trinary::False;
}
Trinary
Bm25Blueprint::lookup_param(const fef::Properties& props, const vespalib::string& param, std::optional<double>& result) const
{
double tmp_result;
auto lres = lookup_param(props, param, tmp_result);
if (lres == Trinary::True) {
result = tmp_result;
}
return lres;
}
double constexpr default_k1_param = 1.2;
double constexpr default_b_param = 0.75;
Bm25Blueprint::Bm25Blueprint()
: Blueprint("bm25"),
_field(nullptr),
_k1_param(default_k1_param),
_b_param(default_b_param),
_avg_field_length()
{
}
void
Bm25Blueprint::visitDumpFeatures(const fef::IIndexEnvironment& env, fef::IDumpFeatureVisitor& visitor) const
{
for (uint32_t i = 0; i < env.getNumFields(); ++i) {
const auto* field = env.getField(i);
if (field->type() == FieldType::INDEX) {
FeatureNameBuilder fnb;
fnb.baseName(getBaseName()).parameter(field->name());
visitor.visitDumpFeature(fnb.buildName());
}
}
}
fef::Blueprint::UP
Bm25Blueprint::createInstance() const
{
return std::make_unique<Bm25Blueprint>();
}
bool
Bm25Blueprint::setup(const fef::IIndexEnvironment& env, const fef::ParameterList& params)
{
const auto& field_name = params[0].getValue();
_field = env.getFieldByName(field_name);
if (lookup_param(env.getProperties(), "k1", _k1_param) == Trinary::Undefined) {
return false;
}
if (lookup_param(env.getProperties(), "b", _b_param) == Trinary::Undefined) {
return false;
}
if (lookup_param(env.getProperties(), "averageFieldLength", _avg_field_length) == Trinary::Undefined) {
return false;
}
describeOutput("score", "The bm25 score for all terms searching in the given index field");
return (_field != nullptr);
}
namespace {
vespalib::string
make_avg_field_length_key(const vespalib::string& base_name, const vespalib::string& field_name)
{
return base_name + ".afl." + field_name;
}
}
void
Bm25Blueprint::prepareSharedState(const fef::IQueryEnvironment& env, fef::IObjectStore& store) const
{
vespalib::string key = make_avg_field_length_key(getBaseName(), _field->name());
if (store.get(key) == nullptr) {
double avg_field_length = _avg_field_length.value_or(env.get_average_field_length(_field->name()));
store.add(key, std::make_unique<AnyWrapper<double>>(avg_field_length));
}
}
fef::FeatureExecutor&
Bm25Blueprint::createExecutor(const fef::IQueryEnvironment& env, vespalib::Stash& stash) const
{
const auto* lookup_result = env.getObjectStore().get(make_avg_field_length_key(getBaseName(), _field->name()));
double avg_field_length = lookup_result != nullptr ?
as_value<double>(*lookup_result) :
_avg_field_length.value_or(env.get_average_field_length(_field->name()));
return stash.create<Bm25Executor>(*_field, env, avg_field_length, _k1_param, _b_param);
}
}
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