GEM-RoBERTa HQ Legal: A Greek Legal Language Model with Quality-Based Data Repetition

Model Description

GEM-RoBERTa HQ Legal is a RoBERTa-base model pre-trained from scratch on a strategically curated 21GB corpus of Greek legal, parliamentary, and governmental text. This model employs an innovative quality-based data repetition strategy, where higher-quality legal sources are repeated multiple times during training to enhance the model's understanding of premium legal terminology and concepts.

This model was trained as part of a research project and has been optimized for downstream tasks such as Named Entity Recognition (NER), Text Classification, and Question Answering within the legal field. The RoBERTa architecture provides enhanced performance through dynamic masking and removal of the Next Sentence Prediction (NSP) task, focusing entirely on Masked Language Modeling (MLM).

How to Get Started

You can use this model directly with the fill-mask pipeline:

from transformers import pipeline

# Load the model
fill_mask = pipeline(
    "fill-mask",
    model="novelcore/gem-roberta-hq-legal",
    tokenizer="novelcore/gem-roberta-hq-legal"
)

# Example from a legal context
text = "Ο κ. Μητσοτάκης <mask> ότι η κυβέρνηση σέβεται πλήρως τις αποφάσεις του Συμβουλίου της Επικρατείας."

# Get predictions
predictions = fill_mask(text)
print(predictions)

For downstream tasks:

from transformers import AutoTokenizer, AutoModelForSequenceClassification

# For legal document classification
tokenizer = AutoTokenizer.from_pretrained("novelcore/gem-roberta-hq-legal")
model = AutoModelForSequenceClassification.from_pretrained("novelcore/gem-roberta-hq-legal")

Training Data

The model was pre-trained on a comprehensive corpus of Greek text compiled from various legal and governmental sources, with a quality-based data repetition strategy that increases exposure to higher-quality legal content. The original 16.75GB corpus was expanded to 21.12GB through strategic repetition.

Quality-Based Data Repetition Strategy

Dataset	Original Size (GB)	Quality Level	Repetition Factor	Effective Size (GB)
Raptarchis Legal Dictionary	0.35	Best	4x	1.40
Political Reports of the Supreme Court	1.20	Medium-Best	3x	3.60
Eur-Lex (Greek Content)	0.92	Medium	2x	1.84
FEK - Greek Government Gazette	11.00	Low	1x	11.00
Greek Parliament Proceedings	2.90	Low-Medium	1x	2.90
Europarl (Greek Content)	0.38	Low	1x	0.38
TOTAL	16.75 GB	-	-	21.12 GB

Rationale for Data Repetition

The quality-based repetition strategy enhances the model's exposure to:

• Premium legal terminology from the Raptarchis Legal Dictionary (4x repetition)
• High-quality judicial reasoning from Supreme Court reports (3x repetition)
• EU legal concepts from Eur-Lex content (2x repetition)

This approach ensures the model develops a stronger understanding of sophisticated legal language while maintaining exposure to the broader legal corpus.

Training Procedure

Model Architecture

The model uses the RoBERTa-base architecture with the following configuration:

• Hidden Size: 768
• Attention Heads: 12
• Hidden Layers: 12
• Parameters: ~125M
• Max Position Embeddings: 514
• Vocabulary Size: 50,264

Preprocessing

The text was tokenized using a custom ByteLevelBPE tokenizer trained from scratch on the Greek legal corpus. The tokenizer uses a vocabulary of 50,264 tokens optimized for Greek legal terminology.

The data was processed into fixed-size chunks of 512 tokens, respecting document boundaries to ensure contextual coherence. Higher-quality sources were strategically repeated during the data preparation phase.

Pre-training

The model was pre-trained from scratch for 150,000 steps on 8x NVIDIA A100 40GB GPUs, using BFloat16 (bf16) mixed-precision for stability and speed. The training took approximately 81 hours and 39 minutes to complete.

The key hyperparameters used were:

• Learning Rate: 1.5e-4 (0.00015) with a linear warmup of 9,000 steps
• Batch Size: Effective batch size of 2,688 (per_device_train_batch_size: 48, gradient_accumulation_steps: 7)
• Optimizer: AdamW with standard parameters
• Weight Decay: 0.01
• Max Sequence Length: 512
• Max Steps: 150,000
• Warmup Steps: 9,000
• MLM Probability: 0.15
• Max Gradient Norm: 1.0

Training Results

The model achieved the following performance metrics:

• Final Training Loss: 0.617
• Final Evaluation Loss: 0.573035
• Training Infrastructure: 8x NVIDIA A100 40GB GPUs
• Total Training Steps: 150,000
• Total Training Time: 66 hours 39 minutes
• Train/Validation Split: 95%/5%
• Effective Training Data: 21.12GB (with quality-based repetition)