Many researchers use the GIZA + + software package ( Och and Ney 2003 ) as a black box , selecting IBM Model 4 as a compromise between alignment quality and efficiency .
a systematic comparison of various statistical alignment models
Franz Josef Och Hermann Ney
IBM Models 3 , 4 , and 5 attempt to capture fertility ( the tendency of each source word to generate several target words ) , resulting in probabilistically deficient , intractable models that require local heuristic search and are difficult to implement and extend . Many researchers use the GIZA + + software package ( Och and Ney 2003 ) as a black box , selecting IBM Model 4 as a compromise between alignment quality and efficiency . All of the models are asymmetric ( switching target and source languages produces drastically different results ) and the simpler models ( IBM Models 1 , 2 , and HMM ) do not enforce bijectivity ( the majority of words translating as a single word ) .
Many researchers use the GIZA + + software package ( @@CITATION ) as a black box , selecting IBM Model 4 as a compromise between alignment quality and efficiency .