Phon Tiers (%xmodsyl, %xphosyl, %xphoaln)

Status: Reference Last updated: 2026-05-11 22:05 EDT

The Phon extension tiers provide syllable-level phonological annotation and segmental alignment between target and actual IPA transcription. They are produced by the Phon application and exported to CHAT via PhonTalk.

Note on the x prefix: These tiers currently use the %x prefix (%xmodsyl, %xphosyl, %xphoaln) to indicate they are user-defined extension tiers, following the Phon project’s convention. When these tiers are officially adopted into the CHAT standard, the x prefix will be dropped.

Background

Phon is a software program for phonological analysis of child language, second language acquisition, and speech disorders. It stores phonological data in its own XML session format with structured IPA transcription, syllabification, and phone-level alignment. When Phon data is exported to CHAT, three extension tiers carry this phonological annotation:

• %xmodsyl — syllabified version of %mod (target/model IPA)
• %xphosyl — syllabified version of %pho (actual IPA)
• %xphoaln — phone-by-phone alignment between target and actual IPA

These tiers are derived views of the parent IPA tiers. The syllabification tiers store the same phoneme sequence as %mod/%pho but with syllable structure annotations applied. There is no independent alignment — the syllabification is a reannotation of the same phone sequence.

Tier Format

%xmodsyl / %xphosyl — Syllabified Phonology

Each phoneme is annotated with a syllable constituent position code:

Format: phone:Position pairs concatenated within each syllable, with . separating syllables within a word and spaces separating words.

*CHI:	I want three cookies .
%mod:	aɪ wɑnt θri kʊkiz .
%xmodsyl:	a:Dɪ:D w:Oɑ:Nn:Ct:C θ:Oɹ:Oi:N k:Oʊ:Nk:Oɪ:Nz:C .
%pho:	aɪ wɑn fwi kʊkiz .
%xphosyl:	a:Dɪ:D w:Oɑ:Nn:C f:Ow:Oi:N k:Oʊ:Nk:Oɪ:Nz:C .

Pauses appear as (.) in the syllabification tiers, matching their representation in %mod/%pho:

%pho:	aɪ (.) wɑnt .
%xphosyl:	a:Dɪ:D (.) w:Oɑ:Nn:Ct:C .

%xphoaln — Phone Alignment

Shows phoneme-by-phoneme correspondence between target (%mod) and actual (%pho) IPA using target↔actual notation. Multiple pairs within a word are comma-separated. ∅ marks deletions (target phone with no actual counterpart) or insertions (actual phone with no target counterpart).

*CHI:	the best .
%mod:	ðə bɛst .
%pho:	ðə bɛs .
%xphoaln:	ð↔ð,ə↔ə b↔b,ɛ↔ɛ,s↔s,t↔∅ .

The %xphoaln tier aligns positionally with both %mod and %pho — word N in %xphoaln corresponds to word N in both parent tiers.

Alignment Semantics

Because the syllabification tiers are derived views, word counts must match:

• %xmodsyl word count = %mod word count
• %xphosyl word count = %pho word count
• %xphoaln word count = %mod word count = %pho word count

Mismatches are flagged as errors E725–E728. See Alignment Architecture for implementation details.

Parsing Strategy

We parse the structure that alignment validation needs, but not the IPA content itself:

• %xmodsyl / %xphosyl: word boundaries are recognized for word-count alignment; the phoneme:Position sequence inside each word stays as an opaque string (talkbank-model::dependent_tier::phon::SylTier’s words: Vec<NonEmptyString>).
• %xphoaln: each word is parsed into a Vec<AlignmentPair>, where AlignmentPair { source: Option<NonEmptyString>, target: Option<NonEmptyString> } represents one source↔target mapping and None represents ∅. Segment topology (which target phone maps to which actual phone, and where insertions / deletions occur) is therefore queryable in code; the IPA characters themselves remain opaque.

Deep phonological analysis is Phon’s domain — we avoid duplicating that work.

Phon XML Source Format

In Phon’s native XML format, phonological data is stored as structured elements:

<ipaTarget>
  <pho>
    <pw>
      <ph scType="onset"><base>θ</base></ph>
      <ph scType="nucleus"><base>ɹ</base></ph>
      <ph scType="nucleus"><base>i</base></ph>
    </pw>
  </pho>
</ipaTarget>

Each <pw> (phonological word) element contains <ph> elements with syllable constituent types (scType). Pauses appear as <pause> elements at the same level as <pw> inside <pho>.

The <alignment> element provides phone-level mappings between target and actual using index-based <pm> (phone map) entries.

Data Quality Notes

A small percentage of Phon corpus XML records have an orthography↔IPA word-count mismatch — i.e. the number of <pw> (phonological word) elements in <ipaTarget> / <ipaActual> differs from the number of <w> elements in <orthography>. This is expected in child phonology data: children may produce extra syllables, partial words, or over-productions relative to the target.

For current counts on the data repos in ~/0tb/data/, run:

python3 scripts/analysis/scan_phon_mismatches.py ~/0tb/data

It reports total XML files scanned, files with at least one mismatched record, and total mismatched records across the corpus.

The PhonTalk CHAT export handles this discrepancy inconsistently:

1. %mod/%pho are written through a OneToOne alignment path that maps IPA words to orthography words — extras are silently dropped
2. %xmodsyl/%xphosyl/%xphoaln are written directly from the raw IPATranscript — all IPA words are included

This produces CHAT files where %xmodsyl may have more words than %mod, triggering E725–E728 validation errors.

This is being investigated in collaboration with the Phon team.