Description
The rules in a TAG are trees with a special leaf node known as the foot node, which is anchored to a word. There are two types of basic trees in TAG: initial trees (often represented as '') and auxiliary trees (''). Initial trees represent basic valency relations, while auxiliary trees allow for recursion. Auxiliary trees have the root (top) node and foot node labeled with the same symbol. A derivation starts with an initial tree, combining via either substitution or adjunction. Substitution replaces a frontier node with another tree whose top node has the same label. Adjunction inserts an auxiliary tree into the center of another tree. The root/foot label of the auxiliary tree must match the label of the node at which it adjoins.
Other variants of TAG allow multi-component trees, trees with multiple foot nodes, and other extensions.
Read more about this topic: Tree-adjoining Grammar
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