Shin-Jye Lee 2021. A Brief Concept of Natural Language Processing: The Chomsky Hierarchy and Hidden Markov Models. iJournals:International Journal of Software & Hardware Research in Engineering ISSN:2347-4890. 9, 6 (Jun. 2021). DOI:https://doi.org/10.26821/IJSHRE.9.6.2021.9614.