Fluid construction grammar

Fluid construction grammar (FCG) is an open-source computational construction grammar formalism that allows computational linguists to formally write down the inventory of lexical and grammatical constructions as well as to do experiments in language learning and language evolution. FCG is an open instrument that can be used by construction grammarians who want to formulate their intuitions and data in a precise way and who want to test the implications of their grammar designs for language parsing, production and learning.

FCG integrates many notions from contemporary computational linguistics such as feature structure and unification-based language processing. Rules are considered bi-directional and hence usable both for parsing and production. Processing is flexible in the sense that it can even cope with partially ungrammatical or incomplete sentences. FCG is called 'fluid' because it acknowledges the premise that language users constantly change and update their grammars. The research on FCG is primarily carried out by Luc Steels and his teams at the VUB AI Lab in Brussels, the Sony Computer Science Lab in Paris and the Language Evolution Lab in Barcelona.

Coupled feature structure

FCG provides two transient feature structure objects that are coupled during a parsing or production operation. One feature structure, designated the 'Left Pole', contains the semantic units. Each named unit is a set of features and their values. The other feature structure, the 'Right Pole', contains the syntactic units. Words are represented by units. Groupings of sub-units into grammatical constructions are also represented by units. The 'subunits' feature links subordinate units into a tree rooted at the 'top' unit. The majority of units in the FCG Left Pole have corresponding same-named units in the Right Pole, thus forming similar unit trees.

During the FCG parse of an utterance, the initial state of the Coupled Feature Structure is for a set of word strings and their ordering to be present on the sole unit of the Right (syntactic) Pole named 'top', and for the Left (semantic) Pole to consist of an empty top unit. As production rules apply consecutively to the Coupled Feature Structure, units and lexical features are linked into the Right Pole tree for each word, and if the word is significant, same-named units with semantic features are added to the Left Pole tree. At the end of a successful parse, the meaning (logical form (linguistics)) is extracted from the 'meaning' features of Left Pole units.

Conversely, because the FCG grammar is bi-directional, the production of an utterance from an initial set of meanings begins with the meanings as feature values of the sole Left Pole unit named 'top'. As successive grammar rules are applied, same-named units are added to both pole trees. At the end of a successful production, the word string is extracted from the 'form' features of Right Pole units.

Linguistic Processing

FCG constructions are a persistent specialization of Coupled Feature Structures, having the additional attributes of type, name, and weight. FCG offers the possibility to apply rules by type, which are distinguished by their name. Weights can be used to choose between competing rules. All constructions (or rules) can be applied in both parsing and production. In production, the left pole of a construction is matched with the corresponding Coupled Feature Structure Left Pole. In parsing, the other direction is chosen, and this time the right pole of a construction is matched with the corresponding Coupled Feature Structure Right Pole.

Flexibility

FCG provides a framework for bi-directional parsing and production. But aside from reserving the 'top' unit name and a few feature names, FCG makes no commitments to any grammatical theory of word categories, and makes no commitment to any particular theory of grammatical constructions. Users of FCG make these choices by writing FCG grammar rules accordingly.

References

• Luc Steels (ed.) (2011). Design Patterns in Fluid Construction Grammar. John Benjamins, Amsterdam.
• Luc Steels (ed.) (in press). Computational Issues in Fluid Construction Grammar. Springer, New York.
• Remi van Trijp, Luc Steels, Katrien Beuls and Pieter Wellens. Fluid Construction Grammar: The New Kid on the Block. Proceedings of the 13th Conference of the European Chapter of the Association for Computational Linguistics, Avignon, 2012. ACL.
• Luc Steels and Joachim De Beule (2006) A (very) Brief Introduction to Fluid Construction Grammar Third International Workshop on Scalable Natural Language Understanding (ScaNaLU 2006) June 8, 2006, following HLT/NAACL, New York City

External links

• http://www.fcg-net.org/ (website of the FCG community, with online demonstrations and chapters of the latest FCG book)
• http://www.emergent-languages.org/ (website on grammar experiments that use FCG).