Twol rules in lttoolbox

Current Status: In Progress
Project: Extend lttoolbox to have the power of HFST

Guidelines

• Every rule in the dictionary file must be properly compatible with the the HFST twolc engine and must not result in any ambiguities.
• The xml tags must be well defined for archiphonemes and rules and must be distinct from the other existing tags in lttoolbox.
• Every rule entry should have comments adequate enough to give a brief understanding of morphophonological transformations performed by the twol compiler.

Design

• The design is still in the development stage and may need significant modifications after it is implemented on the existing language pairs.
• The design must be robust enough to support

Archiphonemes

<archiphoneme>
  <ar n="A" alpha="ae"/>
  <ar n="B" alpha="bcd"/>
</archiphoneme>

Tag/Symbol	Meaning
ar	archiphoneme
alpha	alphabet

Sets

<sets>
  <set n="Vowels" alpha="aeiou"/>
  <set n="BackVow" alpha="bcdfg"/>
</sets>

Tag/Symbol	Meaning
set	set/group of alphabets
n	set name
alpha	alphabet

Twol Rules

<rules>
  <rule c="Back vowel harmony for archiphoneme A">
    <m><ar n="A"></m><s>a</s>
    <context constraint="e"><l_c><set n="BackVow"></l_c><r_c></r_c></context>
  </rule>
  <rule c="Only hyphen in vowel boundaries and caps">
    <m><ar n="hyph?"></m><s>-</s>
    <context constraint="f"><l_c><set n="Vowels"></l_c><r_c></r_c></context>
  </rule>
  <rule c="Back vowel harmony for archiphoneme A">
    <m><ar n="A"></m><s>a</s>
    <context constraint="b"><l_c><set n="BackVow"></l_c><r_c></r_c></context>
  </rule>
  <rule c="Back vowel harmony for archiphoneme A">
    <m><ar n="A"></m><s>a</s>
    <context constraint="ne"><l_c><set n="BackVow"></l_c><r_c></r_c></context>
  </rule>
</rules>

Tag/Symbol	Meaning
rule	twol rule
c	comment
m	morphotactic side
s	surface side
context	context for transformation
constraint	direction constraint
f	a:b => _ ; If the symbol pair a:b appears it must be in context _
b	a:b <= _ ; If lexical a appears in the context _ then it must correspond to surface b
e	a:b <=> _ ; Lexical a always corresponds to b in context _
ne	a:b /<= _ ; Lexical a never corresponds to b in context _
r_c	right context
l_c	left context