segment.1

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.\" $Id: segment.1,v 1.6 2004/12/03 17:59:01 stolcke Exp $
.TH segment 1 "$Date: 2004/12/03 17:59:01 $" "SRILM Tools"
.SH NAME
segment \- segment text using N-gram language model
.SH SYNOPSIS
.B segment
[\c
.BR \-help ]
option
\&...
.SH DESCRIPTION
.B segment
infers a most likely segmentation (location of segment boundaries)
from a text, based on a segment language model.
The language model is a standard backoff N-gram model in ARPA
.BR ngram-format (5),
modeling segmentation using the boundary tags <s> and </s>.
The program reads in a word sequence, finds the most likely locations 
of segment boundaries according to the language model, and 
outputs the word sequence with segment boundaries marked by <s> tags.
.SH OPTIONS
.PP
Each filename argument can be an ASCII file, or a 
compressed file (name ending in .Z or .gz), or ``-'' to indicate
stdin/stdout.
.TP
.B \-help
Print option summary.
.TP
.B \-version
Print version information.
.TP
.BI \-order " n"
Set the maximal N-gram order to be used, by default 3.
NOTE: The order of the model is not set automatically when a model
file is read, so the same file can be used at various orders.
.TP
.BI \-debug " level"
Set the debugging output level (0 means no debugging output).
Debugging messages are sent to stderr.
.TP
.BI \-lm " file"
Read the N-gram model from
.IR file .
.TP
.BI \-text " file"
Find the text to be segmented in 
.IR file .
Default input is stdin.
.TP
.B \-continuous
Process all words in the input as one sequence of words, irrespective of
line breaks.
Normally each line is processed separately as a word sequence.
.TP
.B \-posteriors
Use a forward-backward algorithm to compute the posterior probabilities
of a segment boundary at each word transition, and hypothesize a boundary
whenever the probability exceeds 0.5.
By default a Viterbi algorithm is used that computes
the globally most likely segmentation.
.br
If
.B \-continuous 
is specified as well,
then this option will produce one line of output per word, containing,
respectively, the <s> tag (if appropriate), the word itself, and the 
posterior probability for a boundary preceding the word.
.TP
.B \-unk
Output the unknown word token <unk> for each input word not in the 
language model vocabulary.
The default is to output the input word unchanged.
.TP
.BI \-stag " string"
Use
.I string
to mark segment boundaries in the output.
Default is the start-of-sentence symbol defined in the language model (<s>).
.TP
.BI \-bias " b"
Make a segment boundary a priori more likely by a factor of
.IR b .
This allows balancing of false detection/rejection errors.
The default is 1.
.SH "SEE ALSO"
ngram-count(1), ngram-format(5).
.br
A. Stolcke and E. Shriberg, ``Automatic Linguistic Segmentation of
Spontaneous Speech,'' \fIProc. ICSLP\fP, 1005\-1008, 1996.
.SH BUGS
Only N-grams models up to trigram order are used accurately.
For higher-order models use the more general 
.BR hidden-ngram (1).
.SH AUTHOR
Andreas Stolcke <[e-mail]>.
.br
Copyright 1997\-2004 SRI International