Twol rules in lttoolbox

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Revision as of 09:17, 20 May 2018 by Techievena (talk | contribs) (Add type of rules)
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Current Status: In Progress
Project: Extend lttoolbox to have the power of HFST


  • 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.


  • 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 all type of rules namely:
    • Phonologically conditioned deletion
    • Morphologically conditioned deletion
    • Phonologically conditioned symbol change
    • Morphologically conditioned symbol change
    • Phonologically conditioned insertion
    • Morphologically conditioned insertion


  <ar n="A" alpha="ae"/>
  <ar n="B" alpha="bcd"/>
Tag/Symbol Meaning
ar archiphoneme
alpha alphabet


  <set n="Vowels" alpha="aeiou"/>
  <set n="BackVow" alpha="bcdfg"/>
Tag/Symbol Meaning
set set/group of alphabets
n set name
alpha alphabet

Twol 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 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 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 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>
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