In the 1950’s, when the computer era began, the eminent American linguist Noam Chomsky developed some new formal tools aimed at a better description of facts in various languages [12].
Among the formal tools developed by Chomsky and his followers, the two most important components can be distinguished:
· A purely mathematical nucleus, which includes generative grammars arranged in a hierarchy of grammars of diverse complexity. The generative grammars produce strings of symbols, and sets of these strings are called formal languages, whereas in general linguistics they could be called texts. Chomskian hierarchy is taught to specialists in computer science, usually in a course on languages and automata. This redeems us from necessity to go into any details. The context-free grammars constitute one level of this hierarchy.
· Attempts to describe a number of artificial and natural languages in the framework of generative grammars just mentioned. The phrase structures were formalized as context-free grammars (CFG) and became the basic tool for description of natural languages, in the first place, of English. Just examples of these first attempts are extensively elaborated in the manuals on artificial intelligence. It is a good approach unless a student becomes convinced that it is the only possible.