Tree Adjoining Grammar

Tree - adjoining grammars (TAG), also Baumadjunktions grammars are formal grammars, which were introduced by Aravind Joshi, and are used in computational linguistics for the description of natural languages.

TAGs are similar to context-free grammars, but use trees instead of rules as the smallest elements.

TAGs are considered weak context- sensitive ( mildly context - sensitive) described; so they are stronger than context-free grammars, but weaker than context-sensitive grammars in the Chomsky hierarchy. Therefore, they are probably strong enough to produce natural languages, but also weak enough to still be efficiently parsable.