# The GF Resource Grammar Library

Aarne Ranta 2002-2004

Version 0.6: source package.

Current languages: English, Finnish, French, German, Italian, Russian, Swedish.

News.
10/8/2004 This document updated as a revision of the old resource page.
13/4/2004 Version 0.6 written using the module system of GF 2. Also an extended coverage. The files are placed in separate subdirectories (one per language) and have different names than before, so that file names (without the extension `.gf`) are also legal module names.

Notice. You need GF Version 2.0beta or later to work with these resource grammars. It is available from the GF home page.

## Introduction

As programs in general can be divided into

- application programs
- library programs

GF grammars can be divided into

- application grammars
- resource grammars

An application grammar is typically built around a semantic model, which is formalized as the abstract syntax of the language. Concrete syntax defines a mapping from the abstract syntax into English or Swedish or some other language.

A resource grammar is not based on semantics, but its purpose is to define the linguistic "surface" structures of some language. The availability of these structures makes it easier to write application grammars.

With resource grammars, we aim to achieve division of labour in grammar writing:

- application grammars are written by domain experts
- resource grammars are written by linguists

By using resource grammars, experts of application domains can take linguistic details for granted. For instance, to express the linearization of the arithmetical predicate even in French, she does not have to write

      lin Even x = {s =
          table {
            m => x.s ++
                 table {Ind  => "est" ;  Subj => "soit"} ! m ++
                 table {Masc => "pair" ; Fem  => "paire"} ! x.g
          }
        } ;

but simply

      lin Even = predA1 (adjReg "pair") ;

The author of the French resource grammar will have defined the functions `predAdj` and `adjReg` in such a way that they can be used in all applications.

What is more, the resource grammar has a language-independent API, which makes it possible to write the corresponding rule for other languages in a very similar way. For instance, the German rule is

      lin Even = predA1 (adjReg "gerade") ;

## Coverage

The ultimate goal of the resource grammar library is a full coverage of the linguistic structures of each language. As of Version 0.6, we still have some way to go to reach that goal. But we do have

- fairly complete sets of inflection paradigms for each language
- a representative fragment of syntax covering present-tense indicative, interrogative, and imperative sentence.
- lexica of structural words such as pronouns, articles, conjunctions.

## Demo

To get an idea of the coverage of the resource library, and also to help finding the right functions for your applications, you can do

      make test
      jgf TestAll.gfcm

This opens the syntax editor with all the seven resource grammars extended with a small lexicon.

## Programmer's view on resource grammars

The resource grammar library a hierarchical structure. Its main layers are

- The language-dependent core resources, to be described below.
- The language-independent core resource API, `Combinations.gf`. `Structural.gf`.
- The derived resource libraries, some of which are language-dependent, some of which aren't. The most important ones are the language-dependent lexical paradigm modules `ParadigmsX.gf`.

The core resources should not be needed by application grammarians: it should be enough to use the core resource API and the derived libraries. If this is not the case, the best solution is to extend the derived resource libraries or create new ones.

### Grammaticality guarantee via data abstraction

An important principle is that

- the core resource API and the derived resource libraries guarantee that all type-correct uses of them preserve grammaticality.

This principle is simultaneously a guidance for resource grammarians and an argument for the application grammarian to use these libraries. What we mean by "only using the libraries" is that

- all `lin` and `lincat` rules are built solely from library functions and argument variables.

Thus for instance no records, tables, selections or projections should appear in the rules. What we have achieved then is total data abstraction, and the grammaticality guarantee can be given.

Since the resource grammars are work in progress, their coverage is not yet sufficient for complete data abstraction. In addition, there may of course be bugs in the resource grammars that destroy grammaticality. The GF group is grateful for bug reports, requests, and contributions!

The most important exception to total data abstraction in practice is the incompleteness of resource lexica. Since it is impossible to have full coverage of all the words in a language, users often have to introduce their own lexical entries, and thereby use literal strings in their GF code. The safest and most convenient way of using this is via functions defined in `ParadigmsX.gf` files. Using these functions guarantees that the lexical entries created are type-correct. But nothing guards against misspelling a word, picking a wrong inflectional pattern, or a wrong inherent feature (such as gender).

### The resource grammar documentation in `gfdoc`

All documented GF grammars linked from this page have been written in GF and then translated to HTML using a light-weight documentation tool, `gfdoc`. The tool is available as a part of the GF source code package, in the Haskell file `util/GFDoc.hs` that can be run in the Hugs interpreter by the script `util/gfdoc`. The program also has the flag `+latex`, which produces output in Latex instead of HTML.

### The core resource API

The API is divided into two modules, `Combiantions` and its extension `Structural`.

The file `Combinations.gf` gives the core resource type signatures of phrasal categories and syntactic combination rules, together with some explanations and examples. The examples are so far only in English, but their equivalents are available in all of the languages for which the API has been implemented.

The file `Structurals.gf` gives a list of structural words such as determiners, pronouns, prepositions, and conjunctions.

The file `Structural.gf` cannot be imported directly, but via the generated files `ResourceX.gf` for each language `X`. In these files, the `fun/lin` and `cat/lincat` judgements have been translated into `oper` judgements.

### The lexical paradigm modules

The lexical paradigm modules define, for each lexical category, a worst-case macro for adding words of that category by giving a sufficient number of characteristic forms. In addition, the most common regular paradigms are included, where it is enough just to give one form to generate all the others.

For example, the English paradigm module has the worst-case macro for nouns,

      mkN : (man,men,man's,men's : Str) -> Gender -> N ;

taking four forms and a gender (`human` or `nonhuman`, as is also explained in the module). Its application

      mkN "mouse" "mice" "mouse's" "mice's" nonhuman

defines all information that is needed for the noun mouse. There are also some regular patterns, for instance,

      nReg  : Str -> Gender -> N ;   -- dog, dogs
      nKiss : Str -> Gender -> N ;   -- kiss, kisses

examples of which are

      nReg "car" nonhuman
      nKiss "waitress" human

Here are the documented versions of the paradigm modules:

- English: `ParadigmsEng.gf`
- Finnish: `ParadigmsFin.gf`
- French: `ParadigmsFre.gf`
- German: `ParadigmsGer.gf`
- Italian: `ParadigmsIta.gf`
- Russian: `ParadigmsRus.gf`
- Swedish: `ParadigmsSwe.gf`

### The derived resource libraries

The core resource grammar is minimal in the sense that it defines the smallest syntactic combinations and has no redundancy. For applications, it is usually more convenient to use combinations of the minimal rules. Some such combinations are given in the predication library, which defines the simultaneous applications of one- and two-place verbs and adjectives to all their argument noun phrases. It also defines some other constructions useful for logical and mathematical applications.

The API of the predication library is in the file `Predication.gf`. What is imported is one of the language-dependent files, `X/PredicationX.gf` for each language `X`.

## Linguist's view on resource grammars

### GF and other grammar formalisms

Linguists in particular might be interested in resource grammars for their own sake, not as basis of applications. Since few linguists are so far familiar with GF, we refer to the GF Homepage and especially to the GF Tutorial. What comes here is a brief summary of the relation of GF to other record-based formalisms.

The records of GF are much like feature structures in PATR or HPSG. The main differences are that

- GF has a type system inherited from functional programming languages;
- GF records are primarily obtained as linearizations of trees, not as parses of strings.

The latter difference explains why a GF record typically carries more information than a feature structure. For instance, the record describing the French noun cheval is

      {s = table {Sg => "cheval" ; Pl => "chevaux"} ; g = Masc} ;

showing the full inflection table of the (abstract) noun cheval. A PATR record for the French word cheval would be

      {s = "cheval" ; n = Sg ; g = Masc} ;

showing just the information that can be gathered from the (concrete) string cheval. There is a rather straightforward sense in which the PATR record is an instance of the GF record.

When generating language from syntax trees (or from logical formulas via syntax trees), the record containing full inflection tables is an efficient (linear-time) method of producing the correct forms. This is important when text is generated in real time in an interactive system.

## The structure of core resource grammars

As explained above, the application grammarian's view on resource grammars is through API modules. They are collections of type signatures of functions. It is the task of linguists to define these functions. The definitions are in the end given in the core resource grammars.

We have divided the core resource grammar for each language `X` into the following parts:

- Type system: `TypesX.gf`
- Morphology: `MorphoX.gf`
- Syntax: `SyntaxX.gf`

To get the most powerful resource grammar for each language, one can use these files directly.

However, the languages we have studied have so much in common that we have gathered a considerable set of categories and rules in a multilingual resource grammar. Its parts are

- Abstract syntax: `Resource.gf`
- Language-dependent concrete syntax: `ResourceX.gf` for each language.

The advantage of using this API in application grammars is that their concrete syntax looks the same for all languages up to non-structural words. Thus it is possible to produce concrete syntaxes for new languages without knowing almost anything about them. The abstract syntax serves as a common API to the core resource grammar.

### The code for the core resource grammars

Each language has its resource code in a separate directory. You can view the code as it is, or download it and run `gfdoc` on each file.

- English: `english`
- Finnish: `Finnish`
- Shared Romance: `romance`
- French (building on Romance): `French`
- Italian (building on Romance): `italian`
- Russian: `russian`
- German: `german`
- Swedish: `swedish`

## Compiling and using the resource

To compile the resource into reusable operations, for all languages, type

      make

in the `resource/` directory. This requires that you have a recent version of GF (>= 2.0). What you get is a set of files with names `ResourceX.gfr`, `ResourceX.gfc`, `ParadigmsX.gfr`, and `ParadigmsX.gfc`. You need never consult any of these files, but only look into the documentation.

## Examples of using the resource grammars

### A test suite

The grammars `TestResourceX.gf` define a few expressions of each lexical category and make it possible to test linearization, parsing, random generation, and editing.

### A database query language

The grammars `database/(Database | Restaurant)X.gf` make use of the resource. The `RestaurantX.gf` grammars are just one possible application building on the generic `DatabaseX.gf` grammars. Notice that the `DatabaseX` gramamrs are defined as instantiations of the parametrized module `DatabaseI`.

## Functional morphology

Even though GF is a useful language for describing syntax and semantics, it is not the optimal choice for morphology. One reason is the absence of low-level programming, such as string matching. Another reason is efficiency. In connection with the resource grammar project, we have started another project, functional morphology, which uses Haskell to implement morphology. Haskell morphologies can then be used for generating GF morphologies.

## Further reading

Slides on modular grammar engineering.