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<META NAME="generator" CONTENT="http://txt2tags.sf.net">
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<TITLE>Resource grammar writing HOWTO</TITLE>
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</HEAD><BODY BGCOLOR="white" TEXT="black">
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<P ALIGN="center"><CENTER><H1>Resource grammar writing HOWTO</H1>
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<FONT SIZE="4">
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<I>Author: Aarne Ranta <aarne (at) cs.chalmers.se></I><BR>
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Last update: Fri Jun 23 00:13:11 2006
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</FONT></CENTER>
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<P></P>
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<HR NOSHADE SIZE=1>
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<P></P>
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<UL>
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<LI><A HREF="#toc1">The resource grammar API</A>
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<UL>
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<LI><A HREF="#toc2">Phrase category modules</A>
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<LI><A HREF="#toc3">Infrastructure modules</A>
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<LI><A HREF="#toc4">Lexical modules</A>
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</UL>
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<LI><A HREF="#toc5">Language-dependent syntax modules</A>
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<LI><A HREF="#toc6">The core of the syntax</A>
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<UL>
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<LI><A HREF="#toc7">Another reduced API</A>
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<LI><A HREF="#toc8">The present-tense fragment</A>
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</UL>
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<LI><A HREF="#toc9">Phases of the work</A>
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<UL>
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<LI><A HREF="#toc10">Putting up a directory</A>
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<LI><A HREF="#toc11">Direction of work</A>
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<LI><A HREF="#toc12">The develop-test cycle</A>
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<LI><A HREF="#toc13">Resource modules used</A>
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<LI><A HREF="#toc14">Morphology and lexicon</A>
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<LI><A HREF="#toc15">Lock fields</A>
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<LI><A HREF="#toc16">Lexicon construction</A>
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</UL>
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<LI><A HREF="#toc17">Inside grammar modules</A>
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<UL>
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<LI><A HREF="#toc18">The category system</A>
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<LI><A HREF="#toc19">Phrase category modules</A>
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<LI><A HREF="#toc20">Resource modules</A>
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<LI><A HREF="#toc21">Lexicon</A>
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</UL>
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<LI><A HREF="#toc22">Lexicon extension</A>
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<UL>
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<LI><A HREF="#toc23">The irregularity lexicon</A>
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<LI><A HREF="#toc24">Lexicon extraction from a word list</A>
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<LI><A HREF="#toc25">Lexicon extraction from raw text data</A>
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<LI><A HREF="#toc26">Extending the resource grammar API</A>
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</UL>
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<LI><A HREF="#toc27">Writing an instance of parametrized resource grammar implementation</A>
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<LI><A HREF="#toc28">Parametrizing a resource grammar implementation</A>
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</UL>
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<P></P>
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<HR NOSHADE SIZE=1>
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<P></P>
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<P>
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The purpose of this document is to tell how to implement the GF
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resource grammar API for a new language. We will <I>not</I> cover how
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to use the resource grammar, nor how to change the API. But we
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will give some hints how to extend the API.
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</P>
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<P>
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A manual for using the resource grammar is found in
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</P>
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<P>
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<A HREF="http://www.cs.chalmers.se/~aarne/GF/doc/resource.pdf"><CODE>http://www.cs.chalmers.se/~aarne/GF/doc/resource.pdf</CODE></A>.
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</P>
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<P>
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A tutorial on GF, also introducing the idea of resource grammars, is found in
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</P>
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<P>
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<A HREF="../../../doc/tutorial/gf-tutorial2.html"><CODE>http://www.cs.chalmers.se/~aarne/GF/doc/tutorial/gf-tutorial2.html</CODE></A>.
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</P>
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<P>
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This document concerns the API v. 1.0. You can find the current code in
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</P>
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<P>
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<A HREF=".."><CODE>http://www.cs.chalmers.se/~aarne/GF/lib/resource-1.0/</CODE></A>
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</P>
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<P>
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See the <A HREF="../README"><CODE>README</CODE></A> for
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details on how this differs from previous versions.
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</P>
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<A NAME="toc1"></A>
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<H2>The resource grammar API</H2>
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<P>
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The API is divided into a bunch of <CODE>abstract</CODE> modules.
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The following figure gives the dependencies of these modules.
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</P>
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<P>
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<IMG ALIGN="left" SRC="Grammar.png" BORDER="0" ALT="">
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</P>
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<P>
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Thus the API consists of a grammar and a lexicon, which is
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provided for test purposes.
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</P>
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<P>
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The module structure is rather flat: most modules are direct
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parents of <CODE>Grammar</CODE>. The idea
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is that you can concentrate on one linguistic aspect at a time, or
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also distribute the work among several authors. The module <CODE>Cat</CODE>
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defines the "glue" that ties the aspects together - a type system
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to which all the other modules conform, so that e.g. <CODE>NP</CODE> means
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the same thing in those modules that use <CODE>NP</CODE>s and those that
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constructs them.
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</P>
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<A NAME="toc2"></A>
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<H3>Phrase category modules</H3>
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<P>
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The direct parents of the top will be called <B>phrase category modules</B>,
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since each of them concentrates on a particular phrase category (nouns, verbs,
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adjectives, sentences,...). A phrase category module tells
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<I>how to construct phrases in that category</I>. You will find out that
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all functions in any of these modules have the same value type (or maybe
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one of a small number of different types). Thus we have
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</P>
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<UL>
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<LI><CODE>Noun</CODE>: construction of nouns and noun phrases
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<LI><CODE>Adjective</CODE>: construction of adjectival phrases
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<LI><CODE>Verb</CODE>: construction of verb phrases
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<LI><CODE>Adverb</CODE>: construction of adverbial phrases
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<LI><CODE>Numeral</CODE>: construction of cardinal and ordinal numerals
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<LI><CODE>Sentence</CODE>: construction of sentences and imperatives
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<LI><CODE>Question</CODE>: construction of questions
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<LI><CODE>Relative</CODE>: construction of relative clauses
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<LI><CODE>Conjunction</CODE>: coordination of phrases
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<LI><CODE>Phrase</CODE>: construction of the major units of text and speech
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<LI><CODE>Text</CODE>: construction of texts as sequences of phrases
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<LI><CODE>Idiom</CODE>: idiomatic phrases such as existentials
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</UL>
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<A NAME="toc3"></A>
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<H3>Infrastructure modules</H3>
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<P>
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Expressions of each phrase category are constructed in the corresponding
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phrase category module. But their <I>use</I> takes mostly place in other modules.
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For instance, noun phrases, which are constructed in <CODE>Noun</CODE>, are
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used as arguments of functions of almost all other phrase category modules.
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How can we build all these modules independently of each other?
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</P>
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<P>
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As usual in typeful programming, the <I>only</I> thing you need to know
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about an object you use is its type. When writing a linearization rule
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for a GF abstract syntax function, the only thing you need to know is
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the linearization types of its value and argument categories. To achieve
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the division of the resource grammar to several parallel phrase category modules,
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what we need is an underlying definition of the linearization types. This
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definition is given as the implementation of
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</P>
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<UL>
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<LI><CODE>Cat</CODE>: syntactic categories of the resource grammar
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</UL>
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<P>
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Any resource grammar implementation has first to agree on how to implement
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<CODE>Cat</CODE>. Luckily enough, even this can be done incrementally: you
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can skip the <CODE>lincat</CODE> definition of a category and use the default
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<CODE>{s : Str}</CODE> until you need to change it to something else. In
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English, for instance, many categories do have this linearization type.
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</P>
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<A NAME="toc4"></A>
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<H3>Lexical modules</H3>
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<P>
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What is lexical and what is syntactic is not as clearcut in GF as in
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some other grammar formalisms. Logically, lexical means atom, i.e. a
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<CODE>fun</CODE> with no arguments. Linguistically, one may add to this
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that the <CODE>lin</CODE> consists of only one token (or of a table whose values
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are single tokens). Even in the restricted lexicon included in the resource
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API, the latter rule is sometimes violated in some languages. For instance,
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<CODE>Structural.both7and_DConj</CODE> is an atom, but its linearization is
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two words e.g. <I>both - and</I>.
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</P>
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<P>
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Another characterization of lexical is that lexical units can be added
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almost <I>ad libitum</I>, and they cannot be defined in terms of already
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given rules. The lexical modules of the resource API are thus more like
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samples than complete lists. There are two such modules:
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</P>
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<UL>
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<LI><CODE>Structural</CODE>: structural words (determiners, conjunctions,...)
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<LI><CODE>Lexicon</CODE>: basic everyday content words (nouns, verbs,...)
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</UL>
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<P>
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The module <CODE>Structural</CODE> aims for completeness, and is likely to
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be extended in future releases of the resource. The module <CODE>Lexicon</CODE>
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gives a "random" list of words, which enable interesting testing of syntax,
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and also a check list for morphology, since those words are likely to include
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most morphological patterns of the language.
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</P>
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<P>
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In the case of <CODE>Lexicon</CODE> it may come out clearer than anywhere else
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in the API that it is impossible to give exact translation equivalents in
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different languages on the level of a resource grammar. In other words,
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application grammars are likely to use the resource in different ways for
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different languages.
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</P>
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<A NAME="toc5"></A>
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<H2>Language-dependent syntax modules</H2>
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<P>
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In addition to the common API, there is room for language-dependent extensions
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of the resource. The top level of each languages looks as follows (with English as example):
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</P>
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<PRE>
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abstract English = Grammar, ExtraEngAbs, DictEngAbs
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</PRE>
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<P>
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where <CODE>ExtraEngAbs</CODE> is a collection of syntactic structures specific to English,
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and <CODE>DictEngAbs</CODE> is an English dictionary
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(at the moment, it consists of <CODE>IrregEngAbs</CODE>,
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the irregular verbs of English). Each of these language-specific grammars has
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the potential to grow into a full-scale grammar of the language. These grammar
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can also be used as libraries, but the possibility of using functors is lost.
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</P>
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<P>
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To give a better overview of language-specific structures,
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modules like <CODE>ExtraEngAbs</CODE>
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are built from a language-independent module <CODE>ExtraAbs</CODE>
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by restricted inheritance:
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</P>
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<PRE>
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abstract ExtraEngAbs = Extra [f,g,...]
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</PRE>
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<P>
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Thus any category and function in <CODE>Extra</CODE> may be shared by a subset of all
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languages. One can see this set-up as a matrix, which tells
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what <CODE>Extra</CODE> structures
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are implemented in what languages. For the common API in <CODE>Grammar</CODE>, the matrix
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is filled with 1's (everything is implemented in every language).
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</P>
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<P>
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In a minimal resource grammar implementation, the language-dependent
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extensions are just empty modules, but it is good to provide them for
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the sake of uniformity.
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</P>
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<A NAME="toc6"></A>
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<H2>The core of the syntax</H2>
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<P>
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Among all categories and functions, a handful are
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most important and distinct ones, of which the others are can be
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seen as variations. The categories are
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</P>
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<PRE>
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Cl ; VP ; V2 ; NP ; CN ; Det ; AP ;
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</PRE>
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<P>
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The functions are
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</P>
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<PRE>
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PredVP : NP -> VP -> Cl ; -- predication
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ComplV2 : V2 -> NP -> VP ; -- complementization
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DetCN : Det -> CN -> NP ; -- determination
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ModCN : AP -> CN -> CN ; -- modification
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</PRE>
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<P>
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This <A HREF="latin.gf">toy Latin grammar</A> shows in a nutshell how these
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rules relate the categories to each other. It is intended to be a
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first approximation when designing the parameter system of a new
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language.
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</P>
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<A NAME="toc7"></A>
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<H3>Another reduced API</H3>
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<P>
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If you want to experiment with a small subset of the resource API first,
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try out the module
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<A HREF="http://www.cs.chalmers.se/~aarne/GF/doc/tutorial/resource/Syntax.gf">Syntax</A>
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explained in the
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<A HREF="http://www.cs.chalmers.se/~aarne/GF/doc/tutorial/gf-tutorial2.html">GF Tutorial</A>.
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</P>
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<A NAME="toc8"></A>
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<H3>The present-tense fragment</H3>
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<P>
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Some lines in the resource library are suffixed with the comment
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```--# notpresent
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which is used by a preprocessor to exclude those lines from
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a reduced version of the full resource. This present-tense-only
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version is useful for applications in most technical text, since
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they reduce the grammar size and compilation time. It can also
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be useful to exclude those lines in a first version of resource
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implementation. To compile a grammar with present-tense-only, use
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</P>
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<PRE>
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i -preproc=GF/lib/resource-1.0/mkPresent LangGer.gf
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</PRE>
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<P></P>
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<A NAME="toc9"></A>
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<H2>Phases of the work</H2>
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<A NAME="toc10"></A>
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<H3>Putting up a directory</H3>
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<P>
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Unless you are writing an instance of a parametrized implementation
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(Romance or Scandinavian), which will be covered later, the
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simplest way is to follow roughly the following procedure. Assume you
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are building a grammar for the German language. Here are the first steps,
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which we actually followed ourselves when building the German implementation
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of resource v. 1.0.
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</P>
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<OL>
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<LI>Create a sister directory for <CODE>GF/lib/resource/english</CODE>, named
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<CODE>german</CODE>.
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<PRE>
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cd GF/lib/resource/
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mkdir german
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cd german
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</PRE>
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<P></P>
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<LI>Check out the [ISO 639 3-letter language code
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<A HREF="http://www.w3.org/WAI/ER/IG/ert/iso639.htm">http://www.w3.org/WAI/ER/IG/ert/iso639.htm</A>]
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for German: both <CODE>Ger</CODE> and <CODE>Deu</CODE> are given, and we pick <CODE>Ger</CODE>.
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<P></P>
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<LI>Copy the <CODE>*Eng.gf</CODE> files from <CODE>english</CODE> <CODE>german</CODE>,
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and rename them:
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<PRE>
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cp ../english/*Eng.gf .
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rename 's/Eng/Ger/' *Eng.gf
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</PRE>
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<P></P>
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<LI>Change the <CODE>Eng</CODE> module references to <CODE>Ger</CODE> references
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in all files:
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<PRE>
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sed -i 's/English/German/g' *Ger.gf
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sed -i 's/Eng/Ger/g' *Ger.gf
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</PRE>
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The first line prevents changing the word <CODE>English</CODE>, which appears
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here and there in comments, to <CODE>Gerlish</CODE>.
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<P></P>
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<LI>This may of course change unwanted occurrences of the
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string <CODE>Eng</CODE> - verify this by
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<PRE>
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grep Ger *.gf
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</PRE>
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But you will have to make lots of manual changes in all files anyway!
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<P></P>
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<LI>Comment out the contents of these files:
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<PRE>
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sed -i 's/^/--/' *Ger.gf
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</PRE>
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This will give you a set of templates out of which the grammar
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will grow as you uncomment and modify the files rule by rule.
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<P></P>
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<LI>In all <CODE>.gf</CODE> files, uncomment the module headers and brackets,
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leaving the module bodies commented. Unfortunately, there is no
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simple way to do this automatically (or to avoid commenting these
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lines in the previous step) - but uncommenting the first
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and the last lines will actually do the job for many of the files.
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<P></P>
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<LI>Uncomment the contents of the main grammar file:
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<PRE>
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sed -i 's/^--//' LangGer.gf
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</PRE>
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<P></P>
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<LI>Now you can open the grammar <CODE>LangGer</CODE> in GF:
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<PRE>
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gf LangGer.gf
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</PRE>
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You will get lots of warnings on missing rules, but the grammar will compile.
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<P></P>
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<LI>At all following steps you will now have a valid, but incomplete
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GF grammar. The GF command
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<PRE>
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pg -printer=missing
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</PRE>
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tells you what exactly is missing.
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</OL>
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<P>
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Here is the module structure of <CODE>LangGer</CODE>. It has been simplified by leaving out
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the majority of the phrase category modules. Each of them has the same dependencies
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as e.g. <CODE>VerbGer</CODE>.
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</P>
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<P>
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<IMG ALIGN="middle" SRC="German.png" BORDER="0" ALT="">
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</P>
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<A NAME="toc11"></A>
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<H3>Direction of work</H3>
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<P>
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The real work starts now. There are many ways to proceed, the main ones being
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</P>
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<UL>
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<LI>Top-down: start from the module <CODE>Phrase</CODE> and go down to <CODE>Sentence</CODE>, then
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<CODE>Verb</CODE>, <CODE>Noun</CODE>, and in the end <CODE>Lexicon</CODE>. In this way, you are all the time
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building complete phrases, and add them with more content as you proceed.
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<B>This approach is not recommended</B>. It is impossible to test the rules if
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you have no words to apply the constructions to.
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<P></P>
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<LI>Bottom-up: set as your first goal to implement <CODE>Lexicon</CODE>. To this end, you
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need to write <CODE>ParadigmsGer</CODE>, which in turn needs parts of
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<CODE>MorphoGer</CODE> and <CODE>ResGer</CODE>.
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<B>This approach is not recommended</B>. You can get stuck to details of
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morphology such as irregular words, and you don't have enough grasp about
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the type system to decide what forms to cover in morphology.
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</UL>
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<P>
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The practical working direction is thus a saw-like motion between the morphological
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and top-level modules. Here is a possible course of the work that gives enough
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test data and enough general view at any point:
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</P>
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<OL>
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<LI>Define <CODE>Cat.N</CODE> and the required parameter types in <CODE>ResGer</CODE>. As we define
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<PRE>
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lincat N = {s : Number => Case => Str ; g : Gender} ;
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</PRE>
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we need the parameter types <CODE>Number</CODE>, <CODE>Case</CODE>, and <CODE>Gender</CODE>. The definition
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of <CODE>Number</CODE> in <A HREF="../common/ParamX.gf"><CODE>common/ParamX</CODE></A> works for German, so we
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use it and just define <CODE>Case</CODE> and <CODE>Gender</CODE> in <CODE>ResGer</CODE>.
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<P></P>
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<LI>Define <CODE>regN</CODE> in <CODE>ParadigmsGer</CODE>. In this way you can
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already implement a huge amount of nouns correctly in <CODE>LexiconGer</CODE>. Actually
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just adding <CODE>mkN</CODE> should suffice for every noun - but,
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since it is tedious to use, you
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might proceed to the next step before returning to morphology and defining the
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real work horse <CODE>reg2N</CODE>.
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<P></P>
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<LI>While doing this, you may want to test the resource independently. Do this by
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<PRE>
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i -retain ParadigmsGer
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cc regN "Kirche"
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</PRE>
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<P></P>
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<LI>Proceed to determiners and pronouns in
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<CODE>NounGer</CODE> (<CODE>DetCN UsePron DetSg SgQuant NoNum NoOrd DefArt IndefArt UseN</CODE>)and
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|
<CODE>StructuralGer</CODE> (<CODE>i_Pron every_Det</CODE>). You also need some categories and
|
|
parameter types. At this point, it is maybe not possible to find out the final
|
|
linearization types of <CODE>CN</CODE>, <CODE>NP</CODE>, and <CODE>Det</CODE>, but at least you should
|
|
be able to correctly inflect noun phrases such as <I>every airplane</I>:
|
|
<PRE>
|
|
i LangGer.gf
|
|
l -table DetCN every_Det (UseN airplane_N)
|
|
|
|
Nom: jeder Flugzeug
|
|
Acc: jeden Flugzeug
|
|
Dat: jedem Flugzeug
|
|
Gen: jedes Flugzeugs
|
|
</PRE>
|
|
<P></P>
|
|
<LI>Proceed to verbs: define <CODE>CatGer.V</CODE>, <CODE>ResGer.VForm</CODE>, and
|
|
<CODE>ParadigmsGer.regV</CODE>. You may choose to exclude <CODE>notpresent</CODE>
|
|
cases at this point. But anyway, you will be able to inflect a good
|
|
number of verbs in <CODE>Lexicon</CODE>, such as
|
|
<CODE>live_V</CODE> (<CODE>regV "leven"</CODE>).
|
|
<P></P>
|
|
<LI>Now you can soon form your first sentences: define <CODE>VP</CODE> and
|
|
<CODE>Cl</CODE> in <CODE>CatGer</CODE>, <CODE>VerbGer.UseV</CODE>, and <CODE>SentenceGer.PredVP</CODE>.
|
|
Even if you have excluded the tenses, you will be able to produce
|
|
<PRE>
|
|
i -preproc=mkPresent LangGer.gf
|
|
> l -table PredVP (UsePron i_Pron) (UseV live_V)
|
|
|
|
Pres Simul Pos Main: ich lebe
|
|
Pres Simul Pos Inv: lebe ich
|
|
Pres Simul Pos Sub: ich lebe
|
|
Pres Simul Neg Main: ich lebe nicht
|
|
Pres Simul Neg Inv: lebe ich nicht
|
|
Pres Simul Neg Sub: ich nicht lebe
|
|
</PRE>
|
|
<P></P>
|
|
<LI>Transitive verbs (<CODE>CatGer.V2 ParadigmsGer.dirV2 VerbGer.ComplV2</CODE>)
|
|
are a natural next step, so that you can
|
|
produce <CODE>ich liebe dich</CODE>.
|
|
<P></P>
|
|
<LI>Adjectives (<CODE>CatGer.A ParadigmsGer.regA NounGer.AdjCN AdjectiveGer.PositA</CODE>)
|
|
will force you to think about strong and weak declensions, so that you can
|
|
correctly inflect <I>my new car, this new car</I>.
|
|
<P></P>
|
|
<LI>Once you have implemented the set
|
|
(``Noun.DetCN Noun.AdjCN Verb.UseV Verb.ComplV2 Sentence.PredVP),
|
|
you have overcome most of difficulties. You know roughly what parameters
|
|
and dependences there are in your language, and you can now produce very
|
|
much in the order you please.
|
|
</OL>
|
|
|
|
<A NAME="toc12"></A>
|
|
<H3>The develop-test cycle</H3>
|
|
<P>
|
|
The following develop-test cycle will
|
|
be applied most of the time, both in the first steps described above
|
|
and in later steps where you are more on your own.
|
|
</P>
|
|
<OL>
|
|
<LI>Select a phrase category module, e.g. <CODE>NounGer</CODE>, and uncomment some
|
|
linearization rules (for instance, <CODE>DefSg</CODE>, which is
|
|
not too complicated).
|
|
<P></P>
|
|
<LI>Write down some German examples of this rule, for instance translations
|
|
of "the dog", "the house", "the big house", etc. Write these in all their
|
|
different forms (two numbers and four cases).
|
|
<P></P>
|
|
<LI>Think about the categories involved (<CODE>CN, NP, N</CODE>) and the
|
|
variations they have. Encode this in the lincats of <CODE>CatGer</CODE>.
|
|
You may have to define some new parameter types in <CODE>ResGer</CODE>.
|
|
<P></P>
|
|
<LI>To be able to test the construction,
|
|
define some words you need to instantiate it
|
|
in <CODE>LexiconGer</CODE>. You will also need some regular inflection patterns
|
|
in<CODE>ParadigmsGer</CODE>.
|
|
<P></P>
|
|
<LI>Test by parsing, linearization,
|
|
and random generation. In particular, linearization to a table should
|
|
be used so that you see all forms produced:
|
|
<PRE>
|
|
gr -cat=NP -number=20 -tr | l -table
|
|
</PRE>
|
|
<P></P>
|
|
<LI>Spare some tree-linearization pairs for later regression testing. Use the
|
|
<CODE>tree_bank</CODE> command,
|
|
<PRE>
|
|
gr -cat=NP -number=20 | tb -xml | wf NP.tb
|
|
</PRE>
|
|
You can later compared your modified grammar to this treebank by
|
|
<PRE>
|
|
rf NP.tb | tb -c
|
|
</PRE>
|
|
</OL>
|
|
|
|
<P>
|
|
You are likely to run this cycle a few times for each linearization rule
|
|
you implement, and some hundreds of times altogether. There are 66 <CODE>cat</CODE>s and
|
|
458 <CODE>funs</CODE> in <CODE>Lang</CODE> at the moment; 149 of the <CODE>funs</CODE> are outside the two
|
|
lexicon modules).
|
|
</P>
|
|
<P>
|
|
Here is a <A HREF="../german/log.txt">live log</A> of the actual process of
|
|
building the German implementation of resource API v. 1.0.
|
|
It is the basis of the more detailed explanations, which will
|
|
follow soon. (You will found out that these explanations involve
|
|
a rational reconstruction of the live process! Among other things, the
|
|
API was changed during the actual process to make it more intuitive.)
|
|
</P>
|
|
<A NAME="toc13"></A>
|
|
<H3>Resource modules used</H3>
|
|
<P>
|
|
These modules will be written by you.
|
|
</P>
|
|
<UL>
|
|
<LI><CODE>ResGer</CODE>: parameter types and auxiliary operations
|
|
(a resource for the resource grammar!)
|
|
<LI><CODE>ParadigmsGer</CODE>: complete inflection engine and most important regular paradigms
|
|
<LI><CODE>MorphoGer</CODE>: auxiliaries for <CODE>ParadigmsGer</CODE> and <CODE>StructuralGer</CODE>. This need
|
|
not be separate from <CODE>ResGer</CODE>.
|
|
</UL>
|
|
|
|
<P>
|
|
These modules are language-independent and provided by the existing resource
|
|
package.
|
|
</P>
|
|
<UL>
|
|
<LI><CODE>ParamX</CODE>: parameter types used in many languages
|
|
<LI><CODE>CommonX</CODE>: implementation of language-uniform categories
|
|
such as $Text$ and $Phr$, as well as of
|
|
the logical tense, anteriority, and polarity parameters
|
|
<LI><CODE>Coordination</CODE>: operations to deal with lists and coordination
|
|
<LI><CODE>Prelude</CODE>: general-purpose operations on strings, records,
|
|
truth values, etc.
|
|
<LI><CODE>Predefined</CODE>: general-purpose operations with hard-coded definitions
|
|
</UL>
|
|
|
|
<P>
|
|
An important decision is what rules to implement in terms of operations in
|
|
<CODE>ResGer</CODE>. A golden rule of functional programming says that, whenever
|
|
you find yourself programming by copy and paste, you should write a function
|
|
instead. This indicates that an operation should be created if it is to be
|
|
used at least twice. At the same time, a sound principle of vicinity says that
|
|
it should not require too much browsing to understand what a rule does.
|
|
From these two principles, we have derived the following practice:
|
|
</P>
|
|
<UL>
|
|
<LI>If an operation is needed <I>in two different modules</I>,
|
|
it should be created in <CODE>ResGer</CODE>. An example is <CODE>mkClause</CODE>,
|
|
used in <CODE>Sentence</CODE>, <CODE>Question</CODE>, and <CODE>Relative</CODE>-
|
|
<LI>If an operation is needed <I>twice in the same module</I>, but never
|
|
outside, it should be created in the same module. Many examples are
|
|
found in <CODE>Numerals</CODE>.
|
|
<LI>If an operation is only needed once, it should not be created (but rather
|
|
inlined). Most functions in phrase category modules are implemented in this
|
|
way.
|
|
</UL>
|
|
|
|
<P>
|
|
This discipline is very different from the one followed in earlier
|
|
versions of the library (up to 0.9). We then valued the principle of
|
|
abstraction more than vicinity, creating layers of abstraction for
|
|
almost everything. This led in practice to the duplication of almost
|
|
all code on the <CODE>lin</CODE> and <CODE>oper</CODE> levels, and made the code
|
|
hard to understand and maintain.
|
|
</P>
|
|
<A NAME="toc14"></A>
|
|
<H3>Morphology and lexicon</H3>
|
|
<P>
|
|
The paradigms needed to implement
|
|
<CODE>LexiconGer</CODE> are defined in
|
|
<CODE>ParadigmsGer</CODE>.
|
|
This module provides high-level ways to define the linearization of
|
|
lexical items, of categories <CODE>N, A, V</CODE> and their complement-taking
|
|
variants.
|
|
</P>
|
|
<P>
|
|
For ease of use, the <CODE>Paradigms</CODE> modules follow a certain
|
|
naming convention. Thus they for each lexical category, such as <CODE>N</CODE>,
|
|
the functions
|
|
</P>
|
|
<UL>
|
|
<LI><CODE>mkN</CODE>, for worst-case construction of <CODE>N</CODE>. Its type signature
|
|
has the form
|
|
<PRE>
|
|
mkN : Str -> ... -> Str -> P -> ... -> Q -> N
|
|
</PRE>
|
|
with as many string and parameter arguments as can ever be needed to
|
|
construct an <CODE>N</CODE>.
|
|
<LI><CODE>regN</CODE>, for the most common cases, with just one string argument:
|
|
<PRE>
|
|
regN : Str -> N
|
|
</PRE>
|
|
<LI>A language-dependent (small) set of functions to handle mild irregularities
|
|
and common exceptions.
|
|
<P></P>
|
|
For the complement-taking variants, such as <CODE>V2</CODE>, we provide
|
|
<P></P>
|
|
<LI><CODE>mkV2</CODE>, which takes a <CODE>V</CODE> and all necessary arguments, such
|
|
as case and preposition:
|
|
<PRE>
|
|
mkV2 : V -> Case -> Str -> V2 ;
|
|
</PRE>
|
|
<LI>A language-dependent (small) set of functions to handle common special cases,
|
|
such as direct transitive verbs:
|
|
<PRE>
|
|
dirV2 : V -> V2 ;
|
|
-- dirV2 v = mkV2 v accusative []
|
|
</PRE>
|
|
</UL>
|
|
|
|
<P>
|
|
The golden rule for the design of paradigms is that
|
|
</P>
|
|
<UL>
|
|
<LI>The user will only need function applications with constants and strings,
|
|
never any records or tables.
|
|
</UL>
|
|
|
|
<P>
|
|
The discipline of data abstraction moreover requires that the user of the resource
|
|
is not given access to parameter constructors, but only to constants that denote
|
|
them. This gives the resource grammarian the freedom to change the underlying
|
|
data representation if needed. It means that the <CODE>ParadigmsGer</CODE> module has
|
|
to define constants for those parameter types and constructors that
|
|
the application grammarian may need to use, e.g.
|
|
</P>
|
|
<PRE>
|
|
oper
|
|
Case : Type ;
|
|
nominative, accusative, genitive, dative : Case ;
|
|
</PRE>
|
|
<P>
|
|
These constants are defined in terms of parameter types and constructors
|
|
in <CODE>ResGer</CODE> and <CODE>MorphoGer</CODE>, which modules are not
|
|
visible to the application grammarian.
|
|
</P>
|
|
<A NAME="toc15"></A>
|
|
<H3>Lock fields</H3>
|
|
<P>
|
|
An important difference between <CODE>MorphoGer</CODE> and
|
|
<CODE>ParadigmsGer</CODE> is that the former uses "raw" record types
|
|
for word classes, whereas the latter used category symbols defined in
|
|
<CODE>CatGer</CODE>. When these category symbols are used to denote
|
|
record types in a resource modules, such as <CODE>ParadigmsGer</CODE>,
|
|
a <B>lock field</B> is added to the record, so that categories
|
|
with the same implementation are not confused with each other.
|
|
(This is inspired by the <CODE>newtype</CODE> discipline in Haskell.)
|
|
For instance, the lincats of adverbs and conjunctions are the same
|
|
in <CODE>CommonX</CODE> (and therefore in <CODE>CatGer</CODE>, which inherits it):
|
|
</P>
|
|
<PRE>
|
|
lincat Adv = {s : Str} ;
|
|
lincat Conj = {s : Str} ;
|
|
</PRE>
|
|
<P>
|
|
But when these category symbols are used to denote their linearization
|
|
types in resource module, these definitions are translated to
|
|
</P>
|
|
<PRE>
|
|
oper Adv : Type = {s : Str ; lock_Adv : {}} ;
|
|
oper Conj : Type = {s : Str} ; lock_Conj : {}} ;
|
|
</PRE>
|
|
<P>
|
|
In this way, the user of a resource grammar cannot confuse adverbs with
|
|
conjunctions. In other words, the lock fields force the type checker
|
|
to function as grammaticality checker.
|
|
</P>
|
|
<P>
|
|
When the resource grammar is <CODE>open</CODE>ed in an application grammar, the
|
|
lock fields are never seen (except possibly in type error messages),
|
|
and the application grammarian should never write them herself. If she
|
|
has to do this, it is a sign that the resource grammar is incomplete, and
|
|
the proper way to proceed is to fix the resource grammar.
|
|
</P>
|
|
<P>
|
|
The resource grammarian has to provide the dummy lock field values
|
|
in her hidden definitions of constants in <CODE>Paradigms</CODE>. For instance,
|
|
</P>
|
|
<PRE>
|
|
mkAdv : Str -> Adv ;
|
|
-- mkAdv s = {s = s ; lock_Adv = <>} ;
|
|
</PRE>
|
|
<P></P>
|
|
<A NAME="toc16"></A>
|
|
<H3>Lexicon construction</H3>
|
|
<P>
|
|
The lexicon belonging to <CODE>LangGer</CODE> consists of two modules:
|
|
</P>
|
|
<UL>
|
|
<LI><CODE>StructuralGer</CODE>, structural words, built by directly using
|
|
<CODE>MorphoGer</CODE>.
|
|
<LI><CODE>BasicGer</CODE>, content words, built by using <CODE>ParadigmsGer</CODE>.
|
|
</UL>
|
|
|
|
<P>
|
|
The reason why <CODE>MorphoGer</CODE> has to be used in <CODE>StructuralGer</CODE>
|
|
is that <CODE>ParadigmsGer</CODE> does not contain constructors for closed
|
|
word classes such as pronouns and determiners. The reason why we
|
|
recommend <CODE>ParadigmsGer</CODE> for building <CODE>LexiconGer</CODE> is that
|
|
the coverage of the paradigms gets thereby tested and that the
|
|
use of the paradigms in <CODE>LexiconGer</CODE> gives a good set of examples for
|
|
those who want to build new lexica.
|
|
</P>
|
|
<A NAME="toc17"></A>
|
|
<H2>Inside grammar modules</H2>
|
|
<P>
|
|
Detailed implementation tricks
|
|
are found in the comments of each module.
|
|
</P>
|
|
<A NAME="toc18"></A>
|
|
<H3>The category system</H3>
|
|
<UL>
|
|
<LI><A HREF="gfdoc/Common.html">Common</A>, <A HREF="../common/CommonX.gf">CommonX</A>
|
|
<LI><A HREF="gfdoc/Cat.html">Cat</A>, <A HREF="gfdoc/CatGer.gf">CatGer</A>
|
|
</UL>
|
|
|
|
<A NAME="toc19"></A>
|
|
<H3>Phrase category modules</H3>
|
|
<UL>
|
|
<LI><A HREF="gfdoc/Noun.html">Noun</A>, <A HREF="../german/NounGer.gf">NounGer</A>
|
|
<LI><A HREF="gfdoc/Adjective.html">Adjective</A>, <A HREF="../german/AdjectiveGer.gf">AdjectiveGer</A>
|
|
<LI><A HREF="gfdoc/Verb.html">Verb</A>, <A HREF="../german/VerbGer.gf">VerbGer</A>
|
|
<LI><A HREF="gfdoc/Adverb.html">Adverb</A>, <A HREF="../german/AdverbGer.gf">AdverbGer</A>
|
|
<LI><A HREF="gfdoc/Numeral.html">Numeral</A>, <A HREF="../german/NumeralGer.gf">NumeralGer</A>
|
|
<LI><A HREF="gfdoc/Sentence.html">Sentence</A>, <A HREF="../german/SentenceGer.gf">SentenceGer</A>
|
|
<LI><A HREF="gfdoc/Question.html">Question</A>, <A HREF="../german/QuestionGer.gf">QuestionGer</A>
|
|
<LI><A HREF="gfdoc/Relative.html">Relative</A>, <A HREF="../german/RelativeGer.gf">RelativeGer</A>
|
|
<LI><A HREF="gfdoc/Conjunction.html">Conjunction</A>, <A HREF="../german/ConjunctionGer.gf">ConjunctionGer</A>
|
|
<LI><A HREF="gfdoc/Phrase.html">Phrase</A>, <A HREF="../german/PhraseGer.gf">PhraseGer</A>
|
|
<LI><A HREF="gfdoc/Text.html">Text</A>, <A HREF="../common/TextX.gf">TextX</A>
|
|
<LI><A HREF="gfdoc/Idiom.html">Idiom</A>, <A HREF="../german/IdiomGer.gf">IdiomGer</A>
|
|
<LI><A HREF="gfdoc/Lang.html">Lang</A>, <A HREF="../german/LangGer.gf">LangGer</A>
|
|
</UL>
|
|
|
|
<A NAME="toc20"></A>
|
|
<H3>Resource modules</H3>
|
|
<UL>
|
|
<LI><A HREF="../german/ResGer.gf">ResGer</A>
|
|
<LI><A HREF="../german/MorphoGer.gf">MorphoGer</A>
|
|
<LI><A HREF="gfdoc/ParadigmsGer.html">ParadigmsGer</A>, <A HREF="../german/ParadigmsGer.gf">ParadigmsGer.gf</A>
|
|
</UL>
|
|
|
|
<A NAME="toc21"></A>
|
|
<H3>Lexicon</H3>
|
|
<UL>
|
|
<LI><A HREF="gfdoc/Structural.html">Structural</A>, <A HREF="../german/StructuralGer.gf">StructuralGer</A>
|
|
<LI><A HREF="gfdoc/Lexicon.html">Lexicon</A>, <A HREF="../german/LexiconGer.gf">LexiconGer</A>
|
|
</UL>
|
|
|
|
<A NAME="toc22"></A>
|
|
<H2>Lexicon extension</H2>
|
|
<A NAME="toc23"></A>
|
|
<H3>The irregularity lexicon</H3>
|
|
<P>
|
|
It may be handy to provide a separate module of irregular
|
|
verbs and other words which are difficult for a lexicographer
|
|
to handle. There are usually a limited number of such words - a
|
|
few hundred perhaps. Building such a lexicon separately also
|
|
makes it less important to cover <I>everything</I> by the
|
|
worst-case paradigms (<CODE>mkV</CODE> etc).
|
|
</P>
|
|
<A NAME="toc24"></A>
|
|
<H3>Lexicon extraction from a word list</H3>
|
|
<P>
|
|
You can often find resources such as lists of
|
|
irregular verbs on the internet. For instance, the
|
|
<A HREF="http://www.iee.et.tu-dresden.de/~wernerr/grammar/verben_dt.html">Irregular German Verbs</A>
|
|
page gives a list of verbs in the
|
|
traditional tabular format, which begins as follows:
|
|
</P>
|
|
<PRE>
|
|
backen (du bäckst, er bäckt) backte [buk] gebacken
|
|
befehlen (du befiehlst, er befiehlt; befiehl!) befahl (beföhle; befähle) befohlen
|
|
beginnen begann (begönne; begänne) begonnen
|
|
beißen biß gebissen
|
|
</PRE>
|
|
<P>
|
|
All you have to do is to write a suitable verb paradigm
|
|
</P>
|
|
<PRE>
|
|
irregV : (x1,_,_,_,_,x6 : Str) -> V ;
|
|
</PRE>
|
|
<P>
|
|
and a Perl or Python or Haskell script that transforms
|
|
the table to
|
|
</P>
|
|
<PRE>
|
|
backen_V = irregV "backen" "bäckt" "back" "backte" "backte" "gebacken" ;
|
|
befehlen_V = irregV "befehlen" "befiehlt" "befiehl" "befahl" "beföhle" "befohlen" ;
|
|
</PRE>
|
|
<P></P>
|
|
<P>
|
|
When using ready-made word lists, you should think about
|
|
coyright issues. Ideally, all resource grammar material should
|
|
be provided under GNU General Public License.
|
|
</P>
|
|
<A NAME="toc25"></A>
|
|
<H3>Lexicon extraction from raw text data</H3>
|
|
<P>
|
|
This is a cheap technique to build a lexicon of thousands
|
|
of words, if text data is available in digital format.
|
|
See the <A HREF="http://www.cs.chalmers.se/~markus/FM/">Functional Morphology</A>
|
|
homepage for details.
|
|
</P>
|
|
<A NAME="toc26"></A>
|
|
<H3>Extending the resource grammar API</H3>
|
|
<P>
|
|
Sooner or later it will happen that the resource grammar API
|
|
does not suffice for all applications. A common reason is
|
|
that it does not include idiomatic expressions in a given language.
|
|
The solution then is in the first place to build language-specific
|
|
extension modules. This chapter will deal with this issue (to be completed).
|
|
</P>
|
|
<A NAME="toc27"></A>
|
|
<H2>Writing an instance of parametrized resource grammar implementation</H2>
|
|
<P>
|
|
Above we have looked at how a resource implementation is built by
|
|
the copy and paste method (from English to German), that is, formally
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|
speaking, from scratch. A more elegant solution available for
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families of languages such as Romance and Scandinavian is to
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|
use parametrized modules. The advantages are
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|
</P>
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|
<UL>
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|
<LI>theoretical: linguistic generalizations and insights
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|
<LI>practical: maintainability improves with fewer components
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|
</UL>
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|
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<P>
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|
In this chapter, we will look at an example: adding Italian to
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|
the Romance family (to be completed). Here is a set of
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|
<A HREF="http://www.cs.chalmers.se/~aarne/geocal2006.pdf">slides</A>
|
|
on the topic.
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|
</P>
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|
<A NAME="toc28"></A>
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<H2>Parametrizing a resource grammar implementation</H2>
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<P>
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|
This is the most demanding form of resource grammar writing.
|
|
We do <I>not</I> recommend the method of parametrizing from the
|
|
beginning: it is easier to have one language first implemented
|
|
in the conventional way and then add another language of the
|
|
same family by aprametrization. This means that the copy and
|
|
paste method is still used, but at this time the differences
|
|
are put into an <CODE>interface</CODE> module.
|
|
</P>
|
|
<P>
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|
This chapter will work out an example of how an Estonian grammar
|
|
is constructed from the Finnish grammar through parametrization.
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</P>
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