Constituency Trees
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{{#ev:youtube|https://www.youtube.com/watch?v=y_9SEdG1u3U%7C800%7Ccenter}}
Context Free Grammar
Grammars, generally, are a way of describing a potentially infinite set of strings (sentences) using a finite set of production rules. In a [context-free grammar], production rules take the following form:
V → w
V is a non-terminal symbol (for natural languages, non-terminals usually correspond to **phrases**, such as NP for noun phrases) and w is a (non-empty) string of terminals (words) and nonterminals. It is known that CFGs cannot fully describe natural languages but for MT, they can serve as a very useful simplification.