joseeangel/bert-base-uncased-squad-qa

bert-base-uncased adapted to Extractive QA (SQuAD v1.1) with Full fine-tuning.

Produced for the assignment U2T01 - Adapting BERT for NLP tasks (Trends in Data Science). The delivered method was chosen by measurement, not by default: the table below is the full set of adaptation methods trained for this task, and this repository holds the winner.

Intended use

Extracting the answer span to a question from a paragraph that is known to contain it (SQuAD v1.1 style; the model always returns a span and cannot abstain).

Out of scope: any use where an error carries real cost without a human in the loop, and any language or domain other than the one above.

Training data

• Dataset: rajpurkar/squad (v1.1)
• License: CC BY-SA 4.0
• Citation: Rajpurkar et al. (2016), SQuAD: 100,000+ Questions for Machine Comprehension of Text
• Splits used: {"train": 15000, "dev": 3000, "test": 10570}

Adaptation method

Method	Full fine-tuning
Trainable parameters	108,893,186 of 108,893,186 (100.0%)
Head learning rate	0.001
Encoder learning rate	3e-05
Epochs / batch size	2 / 8 x 2 accumulation steps (effective 16)
Max sequence length	384
Scheduler	linear with 10% warmup
Seed	42
Hardware	Tesla T4 (cuda)
Wall-clock training time	8.3 min

A freshly initialised head and pretrained encoder weights are trained in two parameter groups with separate learning rates; a single shared rate either starves the head or destroys pretrained features.

Evaluation

Held-out test split, never seen during training or model selection.

Metric	Value
F1	82.14
Exact match	72.77

What every method scored on this task

Method	Trainable params	Share of model	F1	Exact match	Train time (min)
Feature-based (linear probe) †	1,538	0.001%	25.18	16.20	25.0
Partial FT (top 4 layers) †	28,353,026	26.037%	72.91	60.68	25.7
Full fine-tuning	108,893,186	100.0%	82.14	72.77	8.3

† trained on Apple M5 instead of Tesla T4. Scores compare across machines; training times do not.

Single run per configuration with a fixed seed. Re-running with a different seed moves these numbers by roughly +/- 1-3 points, so gaps smaller than that are noise rather than findings.

Labels

Start / end position logits over the context tokens.

How to use

from transformers import pipeline

pipe = pipeline("question-answering", model="joseeangel/bert-base-uncased-squad-qa")

Limitations and bias

Trained on a 15 000-example subsample of SQuAD v1.1, so it is below published full-data numbers. It assumes the answer is present in the context: on an unanswerable question it still returns its best span. Contexts longer than 384 subwords are processed in overlapping windows. English only.

The model inherits whatever social bias is present in BERT's pretraining corpus (BooksCorpus + English Wikipedia) and in the task dataset above.

References

• Devlin, Chang, Lee & Toutanova (2019). BERT: Pre-training of Deep Bidirectional Transformers for Language Understanding. arXiv:1810.04805 - section 5.3 is the feature-based vs fine-tuning comparison this work mirrors.
• Rajpurkar et al. (2016), SQuAD: 100,000+ Questions for Machine Comprehension of Text
• HuggingFace Transformers, fine-tune a pretrained model.