Q-systems are a method of

directed graph In mathematics, and more specifically in graph theory, a directed graph (or digraph) is a graph that is made up of a set of vertices connected by directed edges, often called arcs. Definition In formal terms, a directed graph is an ordered pa ...

transformations according to given

grammar In linguistics, the grammar of a natural language is its set of structure, structural constraints on speakers' or writers' composition of clause (linguistics), clauses, phrases, and words. The term can also refer to the study of such constraint ...

rules, developed at the

Université de Montréal The Université de Montréal (UdeM; ; translates to University of Montreal) is a French-language public research university in Montreal, Quebec, Canada. The university's main campus is located in the Côte-des-Neiges neighborhood of Côte-de ...

Alain Colmerauer Alain Colmerauer (24 January 1941 – 12 May 2017) was a French computer scientist. He was a professor at Aix-Marseille University, and the creator of the logic programming language Prolog. Early life Alain Colmerauer was born on 24 January 194 ...

in 1967–70 for use in

natural language processing Natural language processing (NLP) is an interdisciplinary subfield of linguistics, computer science, and artificial intelligence concerned with the interactions between computers and human language, in particular how to program computers to pro ...

. The Université de Montréal's

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system, TAUM-73, used the Q-Systems as its language formalism. The data structure manipulated by a Q-system is a Q-graph, which is a directed acyclic graph with one entry node and one exit node, where each arc bears a labelled ordered tree. An input sentence is usually represented by a linear Q-graph where each arc bears a word (tree reduced to one node labelled by this word). After analysis, the Q-graph is usually a bundle of 1-arc paths, each arc bearing a possible analysis tree. After generation, the goal is usually to produce as many paths as desired outputs, with again one word per arc. A Q-System consists of a sequence of Q-treatments, each being a set of Q-rules, of the form

condition> The Q-treatments are applied in sequence, unless one of them produces the empty Q-graph, in which case the result is the last Q-graph obtained. The three parts of a rule can contain variables for labels, trees, and forests. All variables after "

" must appear in the part. Variables are local to rules. A Q-treatment works in two steps, addition and cleaning. It first applies all its rules exhaustively, using instantiation (one-way unification), thereby adding new paths to the current Q-graph (added arcs and their trees can be used to produce new paths). If and when this addition process halts, all arcs used in some successful rule application are erased, as well as all unused arcs that are no more on any path from the entry node to the exit node. Hence, the result, if any (if the addition step terminates), is again a Q-graph. That allows several Q-Systems to be chained, each of them performing a specialized task, together forming a complex system. For example, TAUM 73 consisted of fifteen chained Q-Systems. An extension of the basic idea of the Q-Systems, namely to replace instantiation by unification (to put it simply, allow "new" variables in the right hand side part of a rule, and replace parametrized labelled trees by logical terms) led to

Prolog Prolog is a logic programming language associated with artificial intelligence and computational linguistics. Prolog has its roots in first-order logic, a formal logic, and unlike many other programming languages, Prolog is intended primarily ...

, designed by

and

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in 1972. Refinements in the other direction (reducing non-determinism and introducing typed labels) by John Chandioux led to GramR, used for programming METEO from 1985 onward. In 2009, Hong Thai Nguyen of GETALP, Laboratoire d'Informatique de Grenoble reimplemented the Q-language in C, using ANTLR to compile the Q-systems and the Q-graphs, and an algorithm proposed by Christian Boitet (as none had been published and sources of the previous Fortran implementation had been lost). That implementation was corrected, completed and extended (to labels using Unicode characters and not only the printable characters of the CDC6600 of the historical version) by David Cattanéo in 2010-11.

References

{{reflist

External links

* http://unldeco.imag.fr/unldeco/SystemsQ.po?localhost=/home/nguyenht/SYS-Q/MONITEUR/] new Q-systems demonstration Computational linguistics Grammar frameworks Linguistic research software

See also

References

Further reading

External links