The linguistic tradition of dependency grammar comprises a large and fairly diverse family of theories and formalisms that share certain basic assumptions about syntactic structure, in particular the assumption that syntactic structure consists of lexical nodes linked by binary relations called dependencies (see, e.g., Tesnière (1959), Sgall (1986), Mel'čuk (1988), Hudson (1990)).
the common formal property of dependency structures, as compared to the representations based on constituency (or phrase structure), is the lack of nonterminal nodes.