What is the difference between link parsing, dependency parsing and constituency parsing?

What is the difference between link parsing, dependency parsing and constituency parsing?


Parsing or syntactic analysis is the process of analysing a string of symbols, either in natural language or in computer languages, conforming to the rules of a formal grammar. The term parsing comes from Latin pars (orationis), meaning part (of speech).


Link grammar (LG) is a theory of syntax… which builds relations between pairs of words, rather than constructing constituents in a tree-like hierarchy. There are two basic parameters: directionality and distance. Link grammar is similar to dependency grammar, but dependency grammar includes a head-dependent relationship, whereas Link Grammar makes the head-dependent relationship optional (Links need not indicate direction).


Dependency grammar (DG) is a class of modern syntactic theories that are all based on the dependency relation (as opposed to the constituency relation)…. Dependency is the notion that linguistic units, e.g. words, are connected to each other by directed links. The (finite) verb is taken to be the structural center of clause structure. All other syntactic units (words) are either directly or indirectly connected to the verb in terms of the directed links, which are called dependencies. DGs are distinct from phrase structure grammars (constituency grammars), since DGs lack phrasal nodes – although they acknowledge phrases. Structure is determined by the relation between a word (a head) and its dependents. Dependency structures are flatter than constituency structures in part because they lack a finite verb phrase constituent, and they are thus well suited for the analysis of languages with free word order.


In a broader sense, phrase structure grammars are also known as constituency grammars. The defining trait of phrase structure grammars is thus their adherence to the constituency relation, as opposed to the dependency relation of dependency grammars.


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