Morphotactic constraints with twol

This page describes how to use twol to implement morphotactic constraints. These are useful for modelling prefix and circumfix morphology.

Prefixes

Let's suppose you have a language like Avar, where the first part of the verb stem changes for gender, for example:

бицине "to speak"
бицуна	neu-иц-aor	it speaks
вицуна	msc-иц-aor	he speaks, I (m.) speak, you (m.) speak
йицуна	fem-иц-aor	she speaks, I (f.) speak, you (f.) speak
рицуна	pl-иц-aor	they speak

So, the obvious thing would be just to put all of the forms in the lexicon, like:

LEXICON AOR

%<aor%>:уна # ;

LEXICON Verbs

бицине%<v%>%<tv%>%<nt%>:биц AOR ;
бицине%<v%>%<tv%>%<m%>:виц AOR ;
бицине%<v%>%<tv%>%<f%>:йиц AOR ;
бицине%<v%>%<tv%>%<pl%>:риц AOR ;

But this is inefficient! What we would like to do is have a single lexicon for the gender prefixes,

LEXICON AOR

%<aor%>:уна # ;

LEXICON Prefixes

%<nt%>:б%> Verbs ;
%<m%>:в%> Verbs ;
%<f%>:й%> Verbs ;
%<pl%>:р%> Verbs ;

LEXICON Verbs

бицине%<v%>%<tv%>:иц AOR ; ! "говорить"

This is great, but we have a problem... The tag for our prefix is in the wrong place!

<nt>бицине<v><tv><aor>:б>ицуна
<m>бицине<v><tv><aor>:в>ицуна
<f>бицине<v><tv><aor>:й>ицуна
<pl>бицине<v><tv><aor>:р>ицуна

See also

• Starting a new language with HFST