Aarne Ranta

Functional morphology

This paper presents a methodology for implementing natural language morphology in the functional language Haskell. The main idea behind is simple: instead of working with untyped regular expressions, which is the state of the art of morphology in computational linguistics, we use finite functions over hereditarily finite algebraic datatypes. The definitions of these datatypes and functions are the language-dependent part of the morphology. The language-independent part consists of an untyped dictionary format which is used for synthesis of word forms, and a decorated trie, which is used for analysis.Functional Morphology builds on ideas introduced by Huet in his computational linguistics toolkit Zen, which he has used to implement the morphology of Sanskrit. The goal has been to make it easy for linguists, who are not trained as functional programmers, to apply the ideas to new languages. As a proof of the productivity of the method, morphologies for Swedish, Italian, Russian, Spanish, and Latin have already been implemented using the library. The Latin morphology is used as a running example in this article.

Grammatical Framework

Grammatical Framework (GF) is a special-purpose functional language for defining grammars. It uses a Logical Framework (LF) for a description of abstract syntax, and adds to this a notation for defining concrete syntax. GF grammars themselves are purely declarative, but can be used both for linearizing syntax trees and parsing strings. GF can describe both formal and natural languages. The key notion of this description is a grammatical object, which is not just a string, but a record that contains all information on inflection and inherent grammatical features such as number and gender in natural languages, or precedence in formal languages. Grammatical objects have a type system, which helps to eliminate run-time errors in language processing. In the same way as a LF, GF uses dependent types in abstract syntax to express semantic conditions, such as well-typedness and proof obligations. Multilingual grammars, where one abstract syntax has many parallel concrete syntaxes, can be used for reliable and meaning-preserving translation. They can also be used in authoring systems, where syntax trees are constructed in an interactive editor similar to proof editors based on LF. While being edited, the trees can simultaneously be viewed in different languages. This paper starts with a gradual introduction to GF, going through a sequence of simpler formalisms till the full power is reached. The introduction is followed by a systematic presentation of the GF formalism and outlines of the main algorithms: partial evaluation and parser generation. The paper concludes by brief discussions of the Haskell implementation of GF, existing applications, and related work.

XML and multilingual document authoring: convergent trends

Typical approaches to XML authoring view a XML document as a mixture of structure (the tags) and surface (text between the tags). We advocate a radical approach where the surface disappears from the XML document altogether to be handled exclusively by rendering mechanisms. This move is based on the view that the authors choices when authoring XML documents are best seen as language-neutral semantic decisions, that the structure can then be viewed as interlingual content, and that the textual output should be derived from this content by language-specific realization mechanisms, thus assimilating XML authoring to Multilingual Document Authoring. However, standard XML tools have important limitations when used for such a purpose: (1) they are weak at propagating semantic dependencies between different parts of the structure, and, (2) current XML rendering tools are ill-suited for handling the grammatical combination of textual units. We present two related proposals for overcoming these limitations: one (GF) originating in the tradition of mathematical proof editors and constructive type theory, the other (IG), a specialization of Definite Clause Grammars strongly inspired by GF.

Implementing controlled languages in GF

This paper introduces GF, Grammatical Framework, as a tool for implementing controlled languages. GF provides a high-level grammar formalism and a resource grammar library that make it easy to write grammars that cover similar fragments in several natural languages at the same time. Authoring help tools and automatic translation are provided for all grammars. As an example, a grammar of Attempto Controlled English is implemented and then ported to Finnish, French, German, Italian and Swedish.

An Authoring Tool for Informal and Formal Requirements Specifications

We describe foundations and design principles of a tool that supports authoring of informal and formal software requirements specifications simultaneously and from a single source. The tool is an attempt to bridge the gap between completely informal requirements specifications (as found in practice) and formal ones (as needed in formal methods). The user is supported by an interactive syntax-directed editor, parsers and linearizers. As a formal specification language we realize the Object Constraint Language, a substandard of the UML, on the informal side a fragment of English. The implementation is based on the Grammatical Framework, a generic tool that combines linguistic and logical methods.

Morphological lexicon extraction from raw text data

The tool extract enables the automatic extraction of lemma-paradigm pairs from raw text data. The tool uses search patterns that consist of regular expressions and propositional logic. These search patterns define sufficient conditions for including lemma-paradigm pairs in the lexicon, on the basis of word forms occurring in the data. This paper explains the search pattern syntax of extract as well as the search algorithm, and discusses the design of search patterns from the recall and precision point of view. The extract tool was developed for morphologies defined in the Functional Morphology tool [1], but it is usable for all systems that implement a word-and-paradigm description of a morphology. The usefulness of the tool is demonstrated by a case study on the Canadian Hansards Corpus of French. The result is evaluated in terms of precision of the extracted lemmas and statistics on coverage and rule productiveness. Competitive extraction figures show that human-written rules in a tailored tool is a time-efficient approach to the task at hand.

Multilingual syntax editing in GF

GF (Grammatical Framework) makes it possible to perform multilingual authoring of documents in restricted languages. The idea is to use an object in type theory to describe the common abstract syntax of a document and then map this object to a concrete syntax in the different languages using linearization functions, one for each language. Incomplete documents are represented using metavariables in type theory. The system belongs to the tradition of logical frameworks in computer science. The paper gives a description of how a user can use the editor to build a document in several languages and also shows some examples how ambiguity is resolved using type checking. There is a brief description of how GF grammars are written for new domains and how linearization functions are defined.

Propositions as games as types

Without violating the spirit of Game-Theoretical semantics, its results can be re-worked in Martin-Löfs Constructive Type Theory by interpreting games as types of Myselfs winning strategies. The philosophical ideas behind Game-Theoretical Semantics in fact highly recommend restricting strategies to effective ones, which is the only controversial step in our interpretation. What is gained, then, is a direct connection between linguistic semantics and computer programming.

Controlled language for everyday use: the MOLTO phrasebook

Controlled languages are usually targeted for technical domains and designed to be unambiguous. This paper presents a controlled language whose domain is touristic phrases, aimed to be usable by anyone without prior training. Despite its informal nature, the language of phrases has a firm notion of semantics, defining the correctness of translations. However, this semantics is formulated in terms of context and situation rather than by logical formulas. Moreover, the language is often ambiguous, and the translation may depend on resolving the ambiguity. This paper shows how to formalize a semantics for tourist phrases and implement it in 15 languages, how to deal with the ambiguities, and how to make the system available for layman users on the web and on mobile phones. While a useful application as such, the Phrasebook also paves the way for an extended notion of controlled language, and the techniques are aimed to be general enough to support many such extensions.

PGF: A Portable Run-time Format for Type-theoretical Grammars

Portable Grammar Format (PGF) is a core language for type-theoretical grammars. It is the target language to which grammars written in the high-level formalism Grammatical Framework (GF) are compiled. Low-level and simple, PGF is easy to reason about, so that its language-theoretic properties can be established. It is also easy to write interpreters that perform parsing and generation with PGF grammars, and compilers converting PGF to other formats. This paper gives a concise description of PGF, covering syntax, semantics, and parser generation. It also discusses the technique of embedded grammars, where language processing tasks defined by PGF grammars are integrated in larger systems.