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trim.lyx
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#LyX 2.0 created this file. For more info see http://www.lyx.org/
\lyxformat 413
\begin_document
\begin_header
\textclass article
\begin_preamble
% vim: tw=70
\usepackage{lrec2006}
% \usepackage[utf8x]{inputenc}
% \usepackage{times}
% \usepackage{url}
% \usepackage[small,bf]{caption}
% \usepackage{latexsym}
\newcommand{\ana}[1]{\texttt{#1}}
\newcommand{\f}[1]{`#1'}
\newcommand{\tool}[1]{\texttt{#1}}
\title{FST Intersection: Ending Dictionary Redundancy in Apertium} % TITLE TODO ugh
% good word: Decomposition
\name{Author1, Author2, Author3}
\address{ Affiliation1, Affiliation2, Affiliation3 \\
Address1, Address2, Address3 \\
author1@xxx.yy, author2@zzz.edu, author3@hhh.com\\}
\abstract{
A Finite State Transducer (FST) used as an analyser, whose output is
input to another FST, may have entries that don't pass through the
second FST. We discuss certain problems that this creates in the
Apertium machine translation platform, and describe the development
of a tool to \emph{trim} such entries. The tool is made part of
Apertium's \tool{lttoolbox} package.
}
\end_preamble
\use_default_options false
\maintain_unincluded_children false
\language english
\language_package none
\inputencoding latin9
\fontencoding default
\font_roman default
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\use_non_tex_fonts false
\font_sc false
\font_osf false
\font_sf_scale 100
\font_tt_scale 100
\graphics default
\default_output_format default
\output_sync 0
\bibtex_command default
\index_command default
\paperfontsize 10
\spacing single
\use_hyperref true
\pdf_bookmarks true
\pdf_bookmarksnumbered false
\pdf_bookmarksopen false
\pdf_bookmarksopenlevel 1
\pdf_breaklinks false
\pdf_pdfborder false
\pdf_colorlinks false
\pdf_backref section
\pdf_pdfusetitle true
\papersize a4paper
\use_geometry false
\use_amsmath 1
\use_esint 1
\use_mhchem 0
\use_mathdots 0
\cite_engine basic
\use_bibtopic false
\use_indices false
\paperorientation portrait
\suppress_date false
\use_refstyle 0
\index Index
\shortcut idx
\color #008000
\end_index
\secnumdepth 3
\tocdepth 3
\paragraph_separation indent
\paragraph_indentation default
\quotes_language english
\papercolumns 1
\papersides 1
\paperpagestyle default
\tracking_changes false
\output_changes false
\html_math_output 0
\html_css_as_file 0
\html_be_strict false
\end_header
\begin_body
\begin_layout Standard
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
maketitleabstract
\end_layout
\end_inset
\end_layout
\begin_layout Section
Introduction and background
\end_layout
\begin_layout Standard
Apertium
\begin_inset space ~
\end_inset
\begin_inset CommandInset citation
LatexCommand cite
key "forcada2011afp"
\end_inset
is a rule-based machine translation platform, where the data and tools
are released under a Free and Open Source license (primarily GNU GPL).
Apertium translators use Finite State Transducers (FST's) for morphological
analysis, bilingual dictionary lookup and generation of surface forms;
most language pairs
\begin_inset Foot
status collapsed
\begin_layout Plain Layout
A
\emph on
language pair
\emph default
is a set of resources to translate between a certain set of languages in
Apertium, e.g.
BasqueâSpanish.
\end_layout
\end_inset
created with Apertium use the
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
tool{
\end_layout
\end_inset
lttoolbox
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
FST library for compiling XML dictionaries into binary FST's and for processing
text with such FST's.
\end_layout
\begin_layout Standard
Below we give some background on how these FST's fit into Apertium as well
as their capabilities; then we discuss the problems that have lead to redundant
dictionary data, and introduce our solution.
\end_layout
\begin_layout Subsection
FST's in the Apertium pipeline
\end_layout
\begin_layout Standard
\begin_inset CommandInset label
LatexCommand label
name "sec:pipeline"
\end_inset
\end_layout
\begin_layout Standard
Translation with Apertium works as a pipeline, where each
\emph on
module
\emph default
processes some text and feeds its output as input to the next module.
First, a surface form like
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
f{
\end_layout
\end_inset
fishes
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
passes through the
\series bold
analyser
\series default
FST module, giving a set of analyses like
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
ana{
\end_layout
\end_inset
fish.n.pl/fish.vblex.pres
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
, or, if it is unknown, simply
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
ana{
\end_layout
\end_inset
*fishes
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
.
Tokenisation is done during analysis, letting the FST decide in a left-right
longest match fashion which words are tokens.
The analyser is technically the union of several FST's, each marked for
whether they contain entries which are tokenised in the regular way (like
regular words), or entries that may separate other tokens, like punctuation.
Anything that has an analysis is a token, and any other sequence consisting
of letters of the
\family typewriter
alphabet
\family default
of the analyser is an unknown word token.
Anything else can separate tokens.
\end_layout
\begin_layout Standard
After analysis, one or more
\series bold
disambiguation
\series default
modules select which of the analyses is the correct one.
The
\series bold
pretransfer
\series default
module does some minor formal changes to do with multiwords.
\end_layout
\begin_layout Standard
Then a disambiguated analysis like
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
ana{
\end_layout
\end_inset
fish.n.pl
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
passes through the
\series bold
bilingual
\series default
FST.
Using EnglishâNorwegian as an example, we would get
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
ana{
\end_layout
\end_inset
fisk.n.m.pl
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
if the bilingual FST had a matching entry, or simply
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
ana{
\end_layout
\end_inset
@fish.n.pl
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
if it was unknown in that dictionary.
So a known entry may get changes to both lemma (
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
ana{
\end_layout
\end_inset
fish
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
â
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
ana{
\end_layout
\end_inset
fisk
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
) and tags (
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
ana{
\end_layout
\end_inset
n.pl
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
â
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
ana{
\end_layout
\end_inset
n.m.pl
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
) by the bilingual FST.
When processing input to the bilingual FST, it is enough that the
\emph on
prefix
\emph default
of the tag sequence matches, so a bilingual dictionary writer can specify
that
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
ana{
\end_layout
\end_inset
fish.n
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
goes to
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
ana{
\end_layout
\end_inset
fisk.n.m
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
and not bother with specifying all inflectional tags like number, definiteness,
tense, and so on.
\end_layout
\begin_layout Standard
The output of the bilingual FST is then passed to the
\series bold
structural transfer
\series default
module (which may change word order, ensure determiner agreement, etc.),
and finally a
\series bold
generator
\series default
FST which turns analyses like
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
ana{
\end_layout
\end_inset
fisk.n.m.pl
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
into forms like
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
f{
\end_layout
\end_inset
fiskar
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
.
Generation is the reverse of analysis; the dictionary which was compiled
into a generator for Norwegian can also be used as an analyser for Norwegian,
by switching the compilation direction.
\end_layout
\begin_layout Standard
A major feature of the
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
tool{
\end_layout
\end_inset
lttoolbox
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
FST package is the support for multiwords and compounds.
A
\series bold
lexical unit
\series default
may be
\end_layout
\begin_layout Itemize
a simple, non-multiword like the noun
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
f{
\end_layout
\end_inset
fish
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
,
\end_layout
\begin_layout Itemize
a space-separated word like the noun
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
f{
\end_layout
\end_inset
hairy frogfish
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
, which will be analysed as one token, but otherwise have no formal differences
from other words,
\end_layout
\begin_layout Itemize
a multiword with inner inflection like
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
f{
\end_layout
\end_inset
takes out
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
, analysed as
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
ana{
\end_layout
\end_inset
take.vblex.pri.p3.sg# out
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
and then turned into
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
ana{
\end_layout
\end_inset
take# out.vblex.pri.p3.sg
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
(the uninflected part is moved onto the lemma) before bilingual dictionary
lookup,
\end_layout
\begin_layout Itemize
a token which is actually two words which should be separated before bilingual
dictionary lookup, like
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
f{
\end_layout
\end_inset
they'll
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
, analysed as
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
ana{
\end_layout
\end_inset
prpers.prn.subj.p3.mf.pl+will.vaux.inf
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
and then split into
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
ana{
\end_layout
\end_inset
prpers.prn.subj.p3.mf.pl
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
and
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
ana{
\end_layout
\end_inset
will.vaux.inf
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
before bilingual dictionary lookup,
\end_layout
\begin_layout Itemize
a combination of these three multiword types, like Catalan
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
f{
\end_layout
\end_inset
creure-ho que
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
, analysed as
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
ana{
\end_layout
\end_inset
creure.vblex.inf+ho.prn.enc.p3.nt# que
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
and then moved and split into
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
ana{
\end_layout
\end_inset
creure# que.vblex.inf
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
and
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
ana{
\end_layout
\end_inset
ho.prn.enc.p3.nt
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
}
\end_layout
\end_inset
before bilingual dictionary lookup.
\end_layout
\begin_layout Standard
In addition to the above multiwords, where the whole string is explicitly
defined as a path in the FST, we have dynamically analysed compounds which
are not defined as single paths in the FST, but still get an analysis during
lookup.
To mark a word as being able to form a compound with words to the right,
we give it the
\begin_inset ERT
status collapsed
\begin_layout Plain Layout
\backslash
f{
\end_layout
\end_inset