NAME

       LucyX::Index::LongFieldSim - Similarity optimized for long fields.

SYNOPSIS

           package MySchema::body;
           use base qw( Lucy::Plan::FullTextType );
           use LucyX::Index::LongFieldSim;
           sub make_similarity { LucyX::Index::LongFieldSim->new }

DESCRIPTION

       Apache Lucy's default Similarity implmentation produces a bias towards extremely short fields.

           Lucy::Index::Similarity

           | more weight
           | *
           |  **
           |    ***
           |       **********
           |                 ********************
           |                                     *******************************
           | less weight                                                        ****
           |------------------------------------------------------------------------
             fewer tokens                                              more tokens

       LongFieldSim eliminates this bias.

           LucyX::Index::LongFieldSim

           | more weight
           |
           |
           |
           |*****************
           |                 ********************
           |                                     *******************************
           | less weight                                                        ****
           |------------------------------------------------------------------------
             fewer tokens                                              more tokens

       In most cases, the default bias towards short fields is desirable.  For instance, say you have two
       documents:

       •   "George Washington"

       •   "George Washington Carver"

       If  a  user  searches  for "george washington", we want the exact title match to appear first.  Under the
       default Similarity implementation it will, because the "Carver" in "George Washington Carver" dilutes the
       impact of the other two tokens.

       However, under LongFieldSim, the two titles  will  yield  equal  scores.   That  would  be  bad  in  this
       particular case, but it could be good in another.

            "George Washington Carver is cool."

            "George Washington Carver was born on the eve of the US Civil War, in
            1864.  His exact date of birth is unknown... Carver's research in crop
            rotation revolutionized agriculture..."

       The  first  document  is  succinct, but useless.  Unfortunately, the default similarity will assess it as
       extremely relevant to a query of "george washington carver".  However,  under  LongFieldSim,  the  short-
       field  bias  is  eliminated,  and  the addition of other mentions of Carver's name in the second document
       yield a higher score and a higher rank.

perl v5.22.1                                       2015-12-18                    LucyX::Index::LongFieldSim(3pm)