A.I. and machine learning era is constantly making our life easier and more comfortable. Undoubtedly, areas which have been developing rapidly in last few years are Natural Language Processing (NLP) and Natural Language Understanding (NLU) which have enabled development of advanced voice assistant devices. However, speech recognition concept is not a recent development - first devices which were capable of recognizing human voice had been presented in 50’s of 20th century by Bell Labs and later by IBM. One of the breakthrough events in A.I. and voice recognition areas took place in February 2011, IBM Watson - a supercomputer capable of understanding and answering natural language questions - took part in popular quiz show “Jeopardy!” [1]. During two-game match it was competing with two best human contestants. IBM Watson defeated them and finally won the main prize - 1 million dollars, which was later given to charities by IBM That was the turning point in compet...