Multi Function Score Query

A query that wraps another query and uses a number of specified functions to modify the document scores. Functions may specify a filter to apply to a subset of recalled documents. How the function scores are combined, and how this final function score modifies the original document score are specified as parameters.

Proto definition:

// A query to modify the score of documents with a given set of functions
message MultiFunctionScoreQuery {
    // Function to produce a weighted value
    message FilterFunction {
        // Apply function only to docs that pass this filter, match all if not specified
        Query filter = 1;
        // Weight to multiply with function score, 1.0 if not specified
        float weight = 2;
        // Function to produce score, will be 1.0 if none are set
        oneof Function {
            // Produce score with score script definition
            Script script = 3;
            // Produce score with a decay function
            DecayFunction decayFunction = 4;
        }
    }

    // Apply decay function to docs
    message DecayFunction {
        // Document field name to use
        string fieldName = 1;
        // Type of decay function to apply
        DecayType decayType = 2;
        // Origin point to calculate the distance
        oneof Origin {
            google.type.LatLng geoPoint = 3;
        }
        // Currently only distance based scale and offset units are supported
        // Distance from origin + offset at which computed score will be equal to decay. Scale should be distance, unit (m, km, mi) with space is optional. Default unit will be meters. Ex: "10", 15 km", "5 m", "7 mi"
        string scale = 4;
        // Compute decay function for docs with a distance greater than offset, will be 0.0 if none is set. Offset should be distance, unit (m, km, mi) with space is optional. Default unit will be meters. Ex: "10", 15 km", "5 m", "7 mi"
        string offset = 5;
        // Defines decay rate for scoring. Should be between (0, 1)
        float decay = 6;
    }

    enum DecayType {
        // Exponential decay function
        DECAY_TYPE_EXPONENTIAL = 0;
        // Linear decay function
        DECAY_TYPE_LINEAR = 1;
        // Gaussian decay function
        DECAY_TYPE_GUASSIAN = 2;
    }


    // How to combine multiple function scores to produce a final function score
    enum FunctionScoreMode {
        // Multiply weighted function scores together
        SCORE_MODE_MULTIPLY = 0;
        // Add weighted function scores together
        SCORE_MODE_SUM = 1;
    }

    // How to combine final function score with query score
    enum BoostMode {
        // Multiply scores together
        BOOST_MODE_MULTIPLY = 0;
        // Add scores together
        BOOST_MODE_SUM = 1;
        // Ignore the query score, and use the function score only
        BOOST_MODE_REPLACE = 2;
    }

    // Main query to produce recalled docs and scores, which will be modified by the final function score
    Query query = 1;
    // Functions to produce final function score
    repeated FilterFunction functions = 2;
    // Method to combine functions scores
    FunctionScoreMode score_mode = 3;
    // Method to modify query document scores with final function score
    BoostMode boost_mode = 4;
    // Optional minimal score to match a document. By default, it's 0.
    float min_score = 5;
    // Determine minimal score is excluded or not. By default, it's false;
    bool min_excluded = 6;
}