Editing Natural language processing (section)

=== Statistical approach ===
In the late 1980s and mid-1990s, the statistical approach ended a period of [[AI winter]], which was caused by the inefficiencies of the rule-based approaches.<ref name="johnson:eacl:ilcl09">[http://www.aclweb.org/anthology/W09-0103 Mark Johnson. How the statistical revolution changes (computational) linguistics.] Proceedings of the EACL 2009 Workshop on the Interaction between Linguistics and Computational Linguistics.</ref><ref name="resnik:langlog11">[http://languagelog.ldc.upenn.edu/nll/?p=2946 Philip Resnik. Four revolutions.] Language Log, February 5, 2011.</ref>

The earliest [[decision tree]]s, producing systems of hard [[Conditional (computer programming)#If–then(–else)|if–then rules]], were still very similar to the old rule-based approaches.
Only the introduction of hidden [[Markov model]]s, applied to part-of-speech tagging, announced the end of the old rule-based approach.