= Syntactic dependency
A <syntactic dependency> is a typed relation between an expression and its <syntactic head> under an explicit grammatical representation. In basic <Universal Dependencies>, the words form a <rooted tree>: one word attaches to a notional `ROOT`, and each other word has one basic head. An enhanced representation can instead form a more general <graph>.<Universal Dependencies annotation guidelines>[Syntax: General Principles, basic tree and enhanced graph]{ref}
For the original example `The small birds fly`, number the words one through four. In head-to-dependent notation, the links are `4→3` for the <subject (grammar)>, `3→1` for the <determiner>, and `3→2` for the <adjective>; `0→4` identifies the sentence head. The determiner link spans a nonadjacent word, showing why dependency is not merely adjacency.
The direction of an arrow and the meaning of each relation must be stated. The project also notes that some dependency labels encode relationships without asserting a simple head-subordinate linguistic analysis. A mechanically valid tree therefore remains a representation to justify, rather than a proof of its own grammatical interpretation.
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