centering-lgram 2.3.1

Discourse Cohesion Analysis Library Based on Centering Theory

Centering-Lgram

Discourse cohesion analysis based on Centering Theory (Grosz, Joshi, and Weinstein, 1983). Measures how entities and topics flow across sentences — pronouns, repetitions, entity continuity.

Note: Cohesion (bağdaşıklık) = surface grammatical/lexical links. Coherence (tutarlılık) = deeper semantic unity. Centering Theory models cohesion.

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⚠️ What This Tool Does NOT Measure

• Factual accuracy — a high cohesion score does NOT mean the content is correct
• Hallucination — a fluent-sounding LLM output can still be completely false
• Overall quality — cohesion is ONE dimension of text quality, not the whole picture

Correct positioning: Use centering-lgram as a complementary evaluator alongside faithfulness/accuracy checkers. It measures "how smoothly does this read?", not "is this correct?".

What we measure	What we DON'T measure
Entity flow across sentences	Factual correctness
Pronoun resolution quality	Hallucination / faithfulness
Topic continuity / shifts	Logical reasoning
Readability (Flesch)	Relevance to prompt
Lexical repetition chains	Domain accuracy

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Quick Start

pip install centering-lgram
python -m spacy download en_core_web_sm

from lgram import TextAnalyzer

ta = TextAnalyzer()
r = ta.analyze("AI helps doctors. It speeds up diagnosis. These tools save lives.")
print(r.overall_cohesion)  # 0.0-1.0 (exact value depends on the spaCy model)
print(r.quality)           # "high"

For best results, use the medium model:

ta = TextAnalyzer("en_core_web_md")

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Genre Calibration

Empirically derived transition patterns. Method: Tukey's fence (p75 + 1.5×IQR).

Brown Corpus (1960s)

NLTK Brown: 1.1M words, 500 files, 15 categories. n=30/genre, HIGH confidence.

Genre	Rough normal (p25–p75)	Flag > (Tukey)	Continue mean	Conf.
Narrative	11.5% – 27.3%	51.0%	49.8%	HIGH
Expository	16.7% – 33.3%	58.2%	29.2%	HIGH
Essay	11.5% – 27.7%	52.0%	30.7%	HIGH

Modern Corpus (2020s) — n=30/genre, HIGH confidence

Genre	Rough normal (p25–p75)	Flag > (Tukey)	Continue mean	Conf.
Narrative	0.0% – 25.0%	62.5%	25.0%	HIGH
Expository	0.0% – 25.0%	62.5%	32.3%	HIGH
Essay	0.0% – 25.0%	62.5%	20.3%	HIGH

Note: Single-author corpus. Stylistic homogeneity may narrow distributions.

Cross-Validation: Wikipedia (multi-author, 2024)

n=12, MEDIUM confidence. Small sample — treat as observational, not conclusive.

Genre	n	Rough normal	Flag >	Continue	Conf.
Expository (Wikipedia)	12	23.0% – 34.6%	52.0%	34.5%	MEDIUM

Wikipedia's 52% flag threshold is broadly consistent with Brown's 58%. Direction is as expected (multi-author corpora cluster together, single-author is the outlier). However, at n=12 this is an observation, not a validated claim. Two caveats: (1) Wikipedia's strict editing guidelines may make it a distinct sub-genre, not representative of general 2020s expository writing. (2) The 6% gap could be measurement noise, temporal change, or genre artifact — the current data cannot distinguish between these explanations.

Findings

1. Rough-Shift >50% is abnormal — all corpora agree. Flag thresholds: 51-63%.
2. Wikipedia cross-validates the multi-author finding — Brown (58%) and Wikipedia (52%) cluster together, while the single-author corpus (63%) diverges. Consistent with the stylistic homogeneity hypothesis. However, n=12 precludes strong conclusions about temporal stability.
3. Wikipedia is not "general 2020s writing" — its strict editing guidelines may constitute a distinct sub-genre. More diverse modern sources needed.

Calibration is reproducible: python -m lgram.brown_calibration

⚠️ Reliability note: Scores depend on the underlying embedding model. For production use, pick ONE model (recommended: en_core_web_md) and standardize on it. Compare texts only within the same genre — cross-genre comparison is meaningless because different genres have different natural transition patterns.

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Core Concepts

Centering Theory tracks three discourse centers per utterance:

Center	Notation	Definition
Forward Centers	Cf	Entities ordered by grammatical salience
Backward Center	Cb	Entity linking to previous utterance
Preferred Center	Cp	Highest-ranked Cf

Five transition types between utterances:

Transition	Rule	Quality
Establish	First utterance	—
Continue	Cb(Ui) = Cb(Ui-1) = Cp(Ui)	Best
Retain	Cb(Ui) = Cb(Ui-1) ≠ Cp(Ui)	Good
Smooth-Shift	Cb(Ui) ≠ Cb(Ui-1) = Cp(Ui)	OK
Rough-Shift	Cb(Ui) ≠ Cb(Ui-1) ≠ Cp(Ui)	Poor

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API — TextAnalyzer (High-Level)

from lgram import TextAnalyzer

ta = TextAnalyzer()                    # default: en_core_web_sm
ta = TextAnalyzer("en_core_web_md")    # better vectors
ta = TextAnalyzer(use_sentence_transformers=True)  # best quality

Core Analysis

Method	Description
analyze(text)	Full analysis → TextReport (sentences, paragraphs, transitions, entities)
analyze_batch(texts, labels)	Compare multiple texts with rankings
analyze_llm(response, prompt?)	LLM output quality: high/medium/low + prompt comparison

Cohesion Metrics

Method	Source	Description
entity_grid_score(text)	Barzilay & Lapata 2005	Entity role persistence (S/O/X/-) across sentences
lexical_chain_score(text)	Halliday & Hasan 1976	Noun repetition + similarity chains
build_cohesion_graph(text)	Graph-based	Sentence adjacency graph (density, centrality, communities)
cohesion_trend(text)	Sliding window	Cohesion change across text (improving/declining/stable)
cohesion_heatmap(text)	Matrix	N×N sentence similarity with weak pair detection
combined_score(text)	Hybrid	Cohesion × 0.6 + Readability × 0.4

Segmentation & Quality

Method	Description
texttile_segments(text)	Hearst 1994 topic segmentation
hybrid_boundaries(text)	Centering + TextTiling intersection (high confidence)
suggest_improvements(text)	Find weak points + fix suggestions
annotate_weak_points(text)	Mark <<<WEAK>>> at cohesion breaks
diff_cohesion(original, revised)	Compare two versions
readability_score(text)	Flesch Reading Ease + statistics

Export

Method	Output
to_dict(report)	JSON-serializable dict
to_json(report)	JSON string
to_summary(report)	Human-readable report

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API — EnhancedCenteringTheory (Low-Level)

from lgram import EnhancedCenteringTheory
import spacy

nlp = spacy.load("en_core_web_sm")
ct = EnhancedCenteringTheory(nlp)

state = ct.analyze_utterance("John went to the store.")
ct.update_discourse("He bought milk.")

result = ct.evaluate_cohesion(["John went.", "He bought milk.", "The store was busy."])

Key methods: compute_forward_centers, compute_backward_center, determine_transition, extract_clauses, detect_boundaries, validate_sequence, visualize, compare_texts, stream_start/feed/flush, save/load, reset.

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CLI

centering-lgram analyze --text "John went to the store. He bought milk."
centering-lgram clauses --text "She left because she was tired."
centering-lgram full --text "John left. He was tired because he worked late."
centering-lgram score --text "Alice met Bob. She greeted him."
centering-lgram info
centering-lgram version

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How It Works

Salience Ranking

Cf ordered by: grammatical role (S=4 > O=3 > other=2 > poss=1) + POS (PRON=3 > PROPN=2 > NOUN=1) + position + entity type (PERSON/ORG/GPE bonus) + pronoun antecedent bonus.

Backward Center (5-level cascade)

1. Possessive scan — "his"/"her" → matched person entity
2. Direct match — entity appears in both Cf lists
3. Pronoun resolution — gender-aware (he→male, she→female)
4. Coreference — entity type matching + vector similarity fallback
5. Compound plural — multiple persons → "they"

Gender-Aware Pronoun Resolution

120+ name gender map (English + Turkish) + title detection (Mr/Mrs) + suffix heuristics. Male pronoun "he" does NOT match female entity "Alice".

Clause Detection

Dependency parse: main, conj, advcl, ccomp, acl, relcl. Separator tokens (commas, conjunctions) assigned to following clause.

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Architecture

lgram/
  __init__.py              # Package exports
  analyzer.py        924   # TextAnalyzer (17 methods)
  benchmark.py       290   # CohesionBenchmark (4 tests)
  cli.py             238   # 6 CLI commands
  core.py              7   # Re-export hub
  utils.py            20   # Logging
  models/
    __init__.py         7   # Sub-package exports
    centering_theory.py 1122 # Core engine
tests/
  test_lgram.py       209   # 15 core tests
  test_edges.py       312   # 34 edge case tests
docs/
  RESEARCH.md                # Literature survey
  IMPLEMENTATION_PLAN.md     # Implementation plan

Dependencies: spacy>=3.4.0 only. Optional: sentence-transformers for MiniLM.

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Use Cases

Domain	Application
LLM Evaluation	Cohesion scoring for GPT/Claude/Llama output
Education	Essay scoring, writing assistant feedback — CAEAS EFL essay feedback tool
Linguistics	Discourse analysis research
Content Quality	Blog/news fluency audits
Translation	Cross-language cohesion comparison
Dialogue	Conversation flow naturalness
Forensics	Statement consistency analysis

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License

MIT — see LICENSE. Copyright (c) 2025 Ilker Atagun.