spacy-fa-pipeline/docs/MODELS.md

The Persian pipelines: what to build, from what, and why

1. What "the 4 English pipelines" actually are

They are one pipeline design at four embedding budgets, not four different products. Every one of them has the same components; the only real axis of variation is where token representations come from.

	en_core_web_sm	en_core_web_md	en_core_web_lg	en_core_web_trf
Size on disk	12 MB	31 MB	382 MB	436 MB
Embeddings	hash embeddings only	685k keys / 20k vectors (300d)	685k keys / 343k vectors (300d)	roberta-base, 768d contextual
Components	tok2vec, tagger, parser, senter, attribute_ruler, lemmatizer, ner	same	same	transformer, tagger, parser, attribute_ruler, lemmatizer, ner
TAG_ACC	0.97	0.97	0.97	0.98
DEP_UAS / LAS	0.92 / 0.90	0.92 / 0.90	0.92 / 0.90	0.95 / 0.94
ENTS_F	0.84	0.85	0.86	0.90
Training data	OntoNotes 5 (+ ClearNLP dep conversion, WordNet 3.0)	+ Explosion vectors (OSCAR 2109 + Wikipedia + OpenSubtitles + WMT News Crawl)	same	OntoNotes 5 + roberta-base

Read the accuracy table honestly: static vectors buy almost nothing for tagging and parsing (identical to two decimals) and ~1–2 F on NER. The transformer buys ~4 LAS and ~6 NER F, at 36× the size and a GPU requirement. That ordering dictates the roadmap below.

Sources: https://spacy.io/models/en.

2. Target: the four Persian pipelines

Naming follows [lang]_[type]_[genre]_[size] (https://spacy.io/models#conventions). core = tagger + parser + lemmatizer + NER. Genre is news, after the dominant genre of UD_Persian-PerDT (its README lists "news fiction nonfiction academic web blog", and spaCy labels comparable treebank-trained pipelines such as de_core_news_sm as news).

Pipeline	Components	Embeddings	Trainable on this hardware?
fa_core_news_sm	tok2vec, tagger, morphologizer, trainable_lemmatizer, parser, ner	hash embeddings	yes — this is what we train now
fa_core_news_md	same	floret vectors, 50k rows	yes, but vectors must be trained first (CPU-days on fa Wikipedia + OSCAR)
fa_core_news_lg	same	floret vectors, 200k rows	same as md, bigger table
fa_core_news_trf	transformer, tagger, morphologizer, trainable_lemmatizer, parser, ner	HooshvareLab/roberta-fa-zwnj-base (Apache-2.0)	no — 2 GB VRAM (GTX 940MX) cannot fine-tune a 125M-param encoder; needs rented GPU

One deviation from the English design, deliberate: Persian gets a morphologizer (UPOS + morphological features) and a trainable_lemmatizer instead of English's attribute_ruler + rule lemmatizer. Reasons:

• The English pipelines use attribute_ruler because OntoNotes gives them PTB tags and they derive UPOS from tags by rule. UD treebanks give UPOS and FEATS as gold data — training a morphologizer on them is strictly more information, and Persian morphology (Number, Person, Tense, Mood, Voice, Polarity, PronType) is worth predicting.
• Persian rule-lemmatizer tables do exist in spacy-lookups-data (fa_lemma_exc.json 1.68 MB, fa_lemma_index.json, fa_lemma_rules.json, derived from Seraji's treebank), but a rule lemmatizer's accuracy is unmeasurable against the corpus it was extracted from and it needs token.pos to work at all. trainable_lemmatizer learns edit trees from PerDT's gold lemmas and reports a real lemma_acc. PerDT yields 1,908 edit trees with 100% lemma coverage — plenty.

senter is intentionally omitted from v1: it is a separately trained component that ships disabled by default in the English pipelines, and the parser already produces sentence boundaries. Adding it later requires only one extra training run.

3. Resource inventory (everything checked for license)

3.1 Treebanks — the tagger / morphologizer / lemmatizer / parser data

Treebank	Sents	Tokens	License	LEMMA	FEATS	XPOS	PROPN?	Verdict
UD_Persian-PerDT (PerUDT v1.0)	29,107	~509k	CC BY-SA 4.0	converted + corrections	converted + corrections	manual native (34 types)	yes	CHOSEN
UD_Persian-Seraji	5,997	~152k	CC BY-SA 4.0	manual native	manual native	manual native (30 types)	no	secondary / cross-eval
UD_Persian-PUD	1,000	—	CC BY-SA 4.0	—	—	none	—	test-only, parallel corpus
UD_Persian-IPerUDT	tiny	—	CC BY-SA 4.0	—	—	none	—	grammar examples, unusable

Measured locally with scripts/inspect_treebanks.py (train splits):

file                             sents    tokens    MWT  empty  lemma%  feats%  UPOS  XPOS  DEP
fa_perdt-ud-train.conllu         26196    452496   6508      0   100.0    57.7    16    34   34
fa_seraji-ud-train.conllu         4798    121067   1117      0   100.0    65.0    15    30   39

Why PerDT over Seraji:

1. 3.7× more training tokens (452k vs 121k). At sm size, data is the binding constraint.
2. Seraji has no PROPN — proper nouns are tagged NOUN. A pipeline that cannot mark proper nouns is crippled for exactly the downstream tasks people use spaCy for.
3. hazm independently chose PerDT for its own spaCy dependency parser — its config.cfg names modified_fa_perdt-ud-train.spacy as the training set. Converging on the same corpus makes our numbers comparable to theirs.

Seraji's advantages (richer manual FEATS, fully manual lemmas) are real; it is the natural cross-evaluation set and a candidate for a future concatenated-corpus run. The two use different XPOS inventories, so naive concatenation would corrupt the tag label space.

3.2 NER — the one place with a licensing minefield

Dataset	Labels	Size	License	Usable?
ParsTwiNER	PER, ORG, LOC, NAT, POG, EVENT	7,667 tweets / 233k tokens	MIT (verified via GitHub API on overfit-ir/parstwiner)	CHOSEN
ARMAN (PersianNER)	6 classes	250k tokens	academic research only	no
PEYMA	7 classes	302k tokens	"free for research purposes", no OSS licence	no
NSURL-2019 Task 7	PEYMA tagset	~1M tokens	no explicit licence	no
HooshvareLab merged ParsNER	10 classes	ARMAN+PEYMA+WikiANN	inherits ARMAN/PEYMA restrictions; HF repo gated (401)	no

This is not pedantry. spaCy's own maintainers state that Persian models trained back in 2018 were never published precisely because of corpus licensing (spaCy discussion #8233, following PR #2797 which added only spacy.blank("fa") tokenizer support). Repeating that mistake would waste the whole exercise: a pipeline you cannot legally redistribute is not a pipeline, it is a local file.

Consequence to state plainly in the model card: the NER component is trained on Twitter text while the rest of the pipeline is trained on edited prose. Expect NER to degrade on formal news text relative to what an ARMAN/PEYMA-trained model would score. That is the price of a redistributable artifact.

3.3 Vectors (for md / lg)

Option	License	Note
floret vectors trained via spacy-vectors-builder (MIT tooling) on fa Wikipedia + OSCAR	corpus-dependent	recommended. Subword + Bloom-hash embeddings: bounded table size, zero OOV
fastText cc.fa.300	CC BY-SA 3.0	quick fallback; classic word table, large and OOV-prone

Floret is the right call for Persian specifically. Persian surface forms explode through suffixation and through inconsistent ZWNJ (U+200C) usage — the same word appears as می‌رود / میرود / می رود in real text. A classic word-vector table has a miss for every variant; floret's subword hashing covers all of them. spaCy already ships floret vectors for Croatian, Finnish, Korean, Slovenian, Swedish and Ukrainian for the same reason.

3.4 Transformer encoders (for trf)

Model	Arch	License	Note
HooshvareLab/roberta-fa-zwnj-base	RoBERTa-base	Apache-2.0	recommended: licensed, ZWNJ-aware, smallest of the credible options
FacebookAI/xlm-roberta-base	XLM-R base, 278M	MIT	licensed but larger
PartAI/TookaBERT-Base	BERT-base	Apache-2.0	licensed
m3hrdadfi/albert-fa-base-v2	ALBERT-base-v2	Apache-2.0	licensed, smallest
HooshvareLab/bert-base-parsbert-uncased	BERT-base, ~162M	no licence on the card	what hazm used; redistribution risk
sbunlp/fabert	BERT-base, 124M	no licence on the card	redistribution risk

All of these are BERT/RoBERTa/XLM-R/ALBERT, so all are supported by both spacy-transformers and spacy-curated-transformers (the latter supports exactly ALBERT / BERT / CamemBERT / RoBERTa / XLM-RoBERTa).

Note the trap: hazm's own pipelines use ParsBERT, which has no license statement. Copying that choice would reintroduce the redistribution problem that sank the 2018 attempt.

4. What already exists (and why it is not enough)

• No trained spaCy Persian pipeline exists. Zero persian / farsi / fa_ hits in spaCy's website/meta/universe.json. spacy.load("fa_core_news_sm") has never worked.
• hazm ships three single-task spaCy pipelines on the HF Hub: hazm-parsbert-postagger (tag_acc 0.9862, hazm's own EZ-augmented tagset), hazm-bert-dependency-parser (dep_uas 0.9246 / dep_las 0.8934, trained on PerDT), hazm-parsbert-chunker (tag_acc 0.9618). Each is transformer + one component, version: 0.0.0, empty license/author/sources, pinned to spaCy 3.6. Using all three means three separate BERT forward passes over the same text and no shared Doc.
• hazm's training code is not reusable. Its trainable models are pycrfsuite CRFs (hazm/sequence_tagger.py); there is no config.cfg or spacy train anywhere in the repo. Its Spacy* classes only download the HF pipelines above.
• hazm's tokenizer is actively incompatible with UD gold tokenization: Normalizer's AFFIX_SPACING_PATTERNS fuse ZWNJ affixes and WordTokenizer.join_verb_parts() glues multi-word verb chains into single underscore-joined tokens. Training against PerDT with hazm's tokenizer would misalign tokens systematically.
• DadmaTools (Apache-2.0 code) emits spaCy-compatible Doc objects but is not a loadable spaCy pipeline package, and its NER wraps ARMAN/PEYMA — the restricted data again.

So what hazm genuinely contributes to this project is one validated design decision (PerDT is the corpus) and the stop-word list already vendored into spacy/lang/fa. Everything else is built with spaCy-native tooling.

5. Decision: train fa_core_news_sm first

Not md/lg: those need floret vectors trained from scratch on Wikipedia+OSCAR (CPU-days) and buy ~0.00 tag/dep accuracy in the English reference numbers. Not trf: 2 GB of VRAM cannot fine-tune a 125M-param encoder, and renting a GPU should wait until the CPU pipeline proves the data plumbing is right. sm is also the tier every other tier is validated against: md/lg/trf reuse the exact same corpus conversion, config skeleton and evaluation harness.

Tokenization decision, settled with a measurement

spaCy has no multi-word-token layer, so CoNLL-U MWT ranges (Persian pronominal clitics and copulas: پدرم = پدر + م) must either be merged into one token or kept split. Measured on the PerDT dev set with scripts/tokenization_report.py, comparing gold boundaries against spacy.blank("fa")'s tokenizer:

spacy convert mode	token P	token R	token F	XPOS types	merge artefacts
--merge-subtokens	0.9860	0.9914	0.9887	68	34 composite tags on 1.49% of tokens; 1.49% lemmas contain a space
plain (clitics split)	0.9875	0.9772	0.9823	35	none

Chosen: --merge-subtokens (also what Explosion's tagger_parser_ud template does). Rationale: without it, 1.5% of gold tokens are boundaries the shipped tokenizer can never produce, so those tokens are permanently unlearnable and unpredictable at runtime. With it, every gold token is reachable; the cost is confined to rare composite XPOS tags such as N_IANM_PR_JOPER (noun + enclitic pronoun) — which are, at least, informative — and 1.5% of lemmas that come out as two words.

The better long-term fix is Persian clitic-splitting suffix rules in spacy/lang/fa, which would be an upstream PR, not a model change. Recorded in docs/CONTRIBUTING-GUIDE.md §5.

Final composition of fa_core_news_sm

Component	Trained on	Metric	Test score
tok2vec	shared, PerDT	—	—
tagger (XPOS)	PerDT, 90 labels	tag_acc	95.96
morphologizer (UPOS + FEATS)	PerDT, 298 labels	pos_acc / morph_acc	96.24 / 96.29
trainable_lemmatizer	PerDT, 1,908 edit trees	lemma_acc	97.91
parser	PerDT, 34 deprels	dep_uas / dep_las	89.69 / 85.15
ner (own internal tok2vec)	ParsTwiNER, 6 labels	ents_p/r/f	74.77 / 61.06 / 67.22

Training cost on the target hardware (4-core i5-7200U, no GPU): 1h27m for the UD components (early-stopped at step 10,800; best checkpoint step 9,200) and ~25 min for NER (best at step 4,000). Both runs are single-threaded, so they were run concurrently. Inference: ~9,250 words/s. Wheel: 13 MB.

The --merge-subtokens artefacts predicted above are visible in the shipped model exactly as expected — کتاب‌هایش ("his/her books") comes out as one token tagged N_IANM_PR_JOPER with lemma کتاب او. Worth knowing before you consume token.lemma_ downstream.

Sources recorded in meta.json, both with their licenses, per https://spacy.io/api/data-formats#meta. CC BY-SA 4.0 on PerDT means the packaged pipeline must carry attribution and share-alike notice — handled in scripts/assemble_core.py.