Lexical functional grammar

The Lexical- Functional Grammar (LFG ) is a Unifikationsgrammatikmodell. It was created in response to the research in the field of transformational grammar and refers mainly to the syntax, morphology and semantics, but not to the phonology. However, ideas from the phonological optimality theory in LFG have been popular recently. The LFG was developed in the 70s by Joan Bresnan and Ronald Kaplan. They wanted to create a grammar model that has enough depth for linguists and simultaneously satisfies the strict formalism of computational linguistics and can be processed by a parser efficiently.

The model

In contrast to Chomsky's syntax, which includes connected by transformations separate levels of linguistic representation, the LFG is based on two mutually limiting structures:

• A Konstituentenbaum ( C structure, English constituent )
• A feature structure (F- structure, english feature )

Constituents are phrases that are inherently related. They are also referred to as a phrase. A set S is usually made of several constituents (eg noun phrases NP, verb phrases VP, adjective phrases AdjP ).

Many syntactic problems can be explained by the incomplete correspondence between these two structures. They have to be combined to form grammatical sentences. Technically speaking: The LFG is contrary to the conditions laid down in recent work on transformational grammar projection principle. Thus, syntactic structures are direct representations of certain lexical information. However LFG provides a more flexible relationship between the syntactic and semantic structure and eliminates the need for transformations.

C- structure ( constituent )

To understand the C structure, we first consider the following simple formal grammar:

The terms noun, articles and verb represent terminal symbols of the grammar. Terminal symbols are usually capitalized small and Nonterminalsymbolen. More specifically, noun, verb and articles Preterminalsymbole. They are merely the precursor to the terminal symbol, they represent a class of terminal symbols. The actual terminal symbols, the words that are not specified in the grammar, but are in a lexicon. If a word in two classes before, it is twice in the lexicon.

With this grammar can the sentence The children develop eating porridge:

This grammar allows sentences like The child eat porridge or cars eat streets. It must be taken into account additional properties such as case, gender, tense, number, and specification.

F- structure ( Features )

Since C - structure alone is not sufficient to produce correct sentences LFG has the additional F- structure. First, we define a dictionary with the additional properties. Properties that are not specified are not yet established.

The above grammar is now extended to a LFG:

The equations indicate that a unification must take place (assignment ). In the F- structure of the parent node of the C structure is unified with the F- structure of the child node. The equation unifies the subject node of the F- structure of the parent node of the C structure with the F- structure of the child node.

We consider again the sentence The children eat porridge and the above mentioned development. However, we consider the process from the perspective of a parser:

The children create an NP node. The children and are an NP node in the C structure. Meanwhile F- structure is created by unifying the F- structures of the and children. The notation of the structures is carried out in so-called attribute-value matrices ( AWMS ):

F by the equation, this structure is unified with the subject of the structure F- S:

This is unified in the end with the F- structure of the VP- node:

The child eating porridge for the given LFG not valid because the F- structure of the NP can not be unified eat with the F- structure:

View

In fact, in the lexicon much more data to be stored. Thus, in children, the specification would be stored revived. Furthermore, stored the underlying lexemes. The dictionary must not be fully listed. Because you can break down words into morphemes, it is often sufficient to store basic forms.