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"""
Legal-BERT Model Architecture - Fully Learning-Based
Includes Hierarchical BERT for document-level understanding
"""
import torch
import torch.nn as nn
import torch.nn.functional as F
from transformers import AutoModel, AutoTokenizer
from typing import Dict, List, Any, Optional, Tuple
class FullyLearningBasedLegalBERT(nn.Module):
"""
Legal-BERT model that learns from discovered risk patterns.
NO hardcoded risk categories!
"""
def __init__(self, config, num_discovered_risks: int = 7):
super().__init__()
self.config = config
self.num_discovered_risks = num_discovered_risks
# Load BERT model
try:
self.bert = AutoModel.from_pretrained(config.bert_model_name)
# Configure BERT dropout
self.bert.config.hidden_dropout_prob = config.dropout_rate
self.bert.config.attention_probs_dropout_prob = config.dropout_rate
except:
# Fallback for testing without transformers
print("β οΈ Warning: Using mock BERT model (transformers not available)")
self.bert = None
# Multi-task heads
hidden_size = 768 # BERT-base hidden size
# Risk classification head (for discovered risk patterns)
self.risk_classifier = nn.Sequential(
nn.Dropout(config.dropout_rate),
nn.Linear(hidden_size, hidden_size // 2),
nn.ReLU(),
nn.Dropout(config.dropout_rate),
nn.Linear(hidden_size // 2, num_discovered_risks)
)
# Severity regression head (0-10 scale)
self.severity_regressor = nn.Sequential(
nn.Dropout(config.dropout_rate),
nn.Linear(hidden_size, hidden_size // 4),
nn.ReLU(),
nn.Dropout(config.dropout_rate),
nn.Linear(hidden_size // 4, 1),
nn.Sigmoid() # Output between 0-1, will be scaled to 0-10
)
# Importance regression head (0-10 scale)
self.importance_regressor = nn.Sequential(
nn.Dropout(config.dropout_rate),
nn.Linear(hidden_size, hidden_size // 4),
nn.ReLU(),
nn.Dropout(config.dropout_rate),
nn.Linear(hidden_size // 4, 1),
nn.Sigmoid() # Output between 0-1, will be scaled to 0-10
)
# Temperature scaling for calibration
self.temperature = nn.Parameter(torch.ones(1))
def forward(self, input_ids: torch.Tensor, attention_mask: torch.Tensor,
output_attentions: bool = False) -> Dict[str, torch.Tensor]:
"""Forward pass through the model
Args:
input_ids: Token IDs from tokenizer
attention_mask: Attention mask for valid tokens
output_attentions: If True, return attention weights for analysis
"""
if self.bert is not None:
# Real BERT forward pass
outputs = self.bert(
input_ids=input_ids,
attention_mask=attention_mask,
output_attentions=output_attentions
)
pooled_output = outputs.pooler_output
attentions = outputs.attentions if output_attentions else None
else:
# Mock output for testing
batch_size = input_ids.size(0)
pooled_output = torch.randn(batch_size, 768)
if input_ids.is_cuda:
pooled_output = pooled_output.cuda()
attentions = None
# Multi-task predictions
risk_logits = self.risk_classifier(pooled_output)
severity_score = self.severity_regressor(pooled_output).squeeze(-1) * 10 # Scale to 0-10
importance_score = self.importance_regressor(pooled_output).squeeze(-1) * 10 # Scale to 0-10
# Apply temperature scaling to classification logits
calibrated_logits = risk_logits / self.temperature
result = {
'risk_logits': risk_logits,
'calibrated_logits': calibrated_logits,
'severity_score': severity_score,
'importance_score': importance_score,
'pooled_output': pooled_output
}
if output_attentions and attentions is not None:
result['attentions'] = attentions
return result
def predict_risk_pattern(self, input_ids: torch.Tensor, attention_mask: torch.Tensor,
return_attentions: bool = False) -> Dict[str, Any]:
"""Make predictions and return interpretable results
Args:
input_ids: Token IDs from tokenizer
attention_mask: Attention mask for valid tokens
return_attentions: If True, include attention weights for analysis
"""
self.eval()
with torch.no_grad():
outputs = self.forward(input_ids, attention_mask, output_attentions=return_attentions)
# Get predictions
risk_probs = torch.softmax(outputs['calibrated_logits'], dim=-1)
predicted_risk = torch.argmax(risk_probs, dim=-1)
confidence = torch.max(risk_probs, dim=-1)[0]
result = {
'predicted_risk_id': predicted_risk.cpu().numpy(),
'risk_probabilities': risk_probs.cpu().numpy(),
'confidence': confidence.cpu().numpy(),
'severity_score': outputs['severity_score'].cpu().numpy(),
'importance_score': outputs['importance_score'].cpu().numpy()
}
if return_attentions and 'attentions' in outputs:
result['attentions'] = outputs['attentions']
return result
def analyze_attention(self, input_ids: torch.Tensor, attention_mask: torch.Tensor,
tokenizer: Optional['LegalBertTokenizer'] = None) -> Dict[str, Any]:
"""Analyze attention patterns to identify important tokens for risk assessment
This method extracts and analyzes BERT attention weights to determine which
tokens/words contribute most to the risk prediction. Useful for interpretability.
Args:
input_ids: Token IDs from tokenizer
attention_mask: Attention mask for valid tokens
tokenizer: Tokenizer to decode tokens (optional)
Returns:
Dictionary containing:
- token_importance: Per-token importance scores
- top_tokens: Most important tokens for prediction
- attention_weights: Raw attention weights from last layer
- layer_analysis: Attention analysis per layer
"""
self.eval()
with torch.no_grad():
outputs = self.forward(input_ids, attention_mask, output_attentions=True)
if 'attentions' not in outputs or outputs['attentions'] is None:
return {'error': 'Attention weights not available'}
attentions = outputs['attentions'] # Tuple of (batch, num_heads, seq_len, seq_len)
batch_size, seq_len = input_ids.shape
# Average attention across all heads and layers for each token
# Shape: (num_layers, batch, num_heads, seq_len, seq_len)
all_attentions = torch.stack(attentions) # Stack all layers
# Get attention to [CLS] token (index 0) which is used for classification
# Average across layers and heads
cls_attention = all_attentions[:, :, :, 0, :].mean(dim=[0, 2]) # (batch, seq_len)
# Also get average attention from all tokens (global importance)
global_attention = all_attentions.mean(dim=[0, 2, 3]) # (batch, seq_len)
# Combine CLS attention and global attention for final importance score
token_importance = (cls_attention + global_attention) / 2
# Mask out padding tokens
token_importance = token_importance * attention_mask
# Get top-k most important tokens per sample
k = min(10, seq_len)
top_values, top_indices = torch.topk(token_importance, k, dim=1)
result = {
'token_importance': token_importance.cpu().numpy(),
'top_token_indices': top_indices.cpu().numpy(),
'top_token_scores': top_values.cpu().numpy(),
'attention_weights': {
'cls_attention': cls_attention.cpu().numpy(),
'global_attention': global_attention.cpu().numpy()
}
}
# Add layer-wise analysis
layer_attentions = []
for layer_idx, layer_attn in enumerate(attentions):
# Average across heads and get attention to CLS token
layer_cls_attn = layer_attn[:, :, 0, :].mean(dim=1) # (batch, seq_len)
layer_attentions.append({
'layer': layer_idx,
'cls_attention': layer_cls_attn.cpu().numpy()
})
result['layer_analysis'] = layer_attentions
# Decode tokens if tokenizer provided
if tokenizer is not None and tokenizer.tokenizer is not None:
tokens = tokenizer.tokenizer.convert_ids_to_tokens(input_ids[0])
top_tokens = [tokens[idx] for idx in top_indices[0].cpu().numpy()]
result['tokens'] = tokens
result['top_tokens'] = top_tokens
return result
class LegalBertTokenizer:
"""Tokenizer wrapper for Legal-BERT"""
def __init__(self, model_name: str = "bert-base-uncased"):
try:
self.tokenizer = AutoTokenizer.from_pretrained(model_name)
except:
print("β οΈ Warning: Using mock tokenizer (transformers not available)")
self.tokenizer = None
def tokenize_clauses(self, clauses: List[str], max_length: int = 512) -> Dict[str, torch.Tensor]:
"""Tokenize legal clauses for model input"""
if self.tokenizer is None:
# Mock tokenization for testing
batch_size = len(clauses)
return {
'input_ids': torch.randint(0, 1000, (batch_size, max_length)),
'attention_mask': torch.ones(batch_size, max_length)
}
# Real tokenization
encoded = self.tokenizer(
clauses,
padding=True,
truncation=True,
max_length=max_length,
return_tensors='pt'
)
return {
'input_ids': encoded['input_ids'],
'attention_mask': encoded['attention_mask']
}
def decode_tokens(self, token_ids: torch.Tensor) -> List[str]:
"""Decode token IDs back to text"""
if self.tokenizer is None:
return ["Mock decoded text"] * token_ids.size(0)
return self.tokenizer.batch_decode(token_ids, skip_special_tokens=True)
# ============================================================================
# HIERARCHICAL BERT FOR DOCUMENT-LEVEL UNDERSTANDING
# ============================================================================
class HierarchicalLegalBERT(nn.Module):
"""
Hierarchical BERT for document-level contract understanding
**Key Innovation**: Processes documents hierarchically to maintain context
Architecture:
Clause Encoding (BERT) β Section Aggregation (LSTM+Attention) β Document
Solves the context problem:
- Your current model: Each clause processed independently β
- This model: Clauses processed WITH section context β
Usage:
# Training: Same as current model (clause-level labels)
# Inference: Processes full documents with context
document = [
['clause1', 'clause2'], # Section 1
['clause3', 'clause4'], # Section 2
]
results = model.predict_document(document)
"""
def __init__(
self,
config,
num_discovered_risks: int = 7,
hidden_dim: int = 256,
num_lstm_layers: int = 2
):
super().__init__()
self.config = config
self.num_discovered_risks = num_discovered_risks
self.hidden_dim = hidden_dim
# Load BERT for clause encoding
try:
self.bert = AutoModel.from_pretrained(config.bert_model_name)
self.bert.config.hidden_dropout_prob = config.dropout_rate
self.bert.config.attention_probs_dropout_prob = config.dropout_rate
self.bert_hidden_size = self.bert.config.hidden_size # 768
except:
print("β οΈ Warning: Using mock BERT model")
self.bert = None
self.bert_hidden_size = 768
# Hierarchical LSTM layers
# Level 1: Clause-to-Section (captures context within a section)
self.clause_to_section = nn.LSTM(
input_size=self.bert_hidden_size,
hidden_size=hidden_dim,
num_layers=num_lstm_layers,
bidirectional=True,
dropout=config.dropout_rate if num_lstm_layers > 1 else 0,
batch_first=True
)
# Level 2: Section-to-Document (captures context across sections)
self.section_to_document = nn.LSTM(
input_size=hidden_dim * 2, # Bidirectional
hidden_size=hidden_dim,
num_layers=num_lstm_layers,
bidirectional=True,
dropout=config.dropout_rate if num_lstm_layers > 1 else 0,
batch_first=True
)
# Attention mechanisms for interpretability
self.clause_attention = nn.Sequential(
nn.Linear(hidden_dim * 2, hidden_dim),
nn.Tanh(),
nn.Dropout(config.dropout_rate),
nn.Linear(hidden_dim, 1)
)
self.section_attention = nn.Sequential(
nn.Linear(hidden_dim * 2, hidden_dim),
nn.Tanh(),
nn.Dropout(config.dropout_rate),
nn.Linear(hidden_dim, 1)
)
# Task-specific prediction heads (same as your current model)
# These operate on context-aware clause representations
self.risk_classifier = nn.Sequential(
nn.Dropout(config.dropout_rate),
nn.Linear(hidden_dim * 2, hidden_dim),
nn.ReLU(),
nn.Dropout(config.dropout_rate),
nn.Linear(hidden_dim, num_discovered_risks)
)
self.severity_regressor = nn.Sequential(
nn.Dropout(config.dropout_rate),
nn.Linear(hidden_dim * 2, hidden_dim // 2),
nn.ReLU(),
nn.Dropout(config.dropout_rate),
nn.Linear(hidden_dim // 2, 1),
nn.Sigmoid()
)
self.importance_regressor = nn.Sequential(
nn.Dropout(config.dropout_rate),
nn.Linear(hidden_dim * 2, hidden_dim // 2),
nn.ReLU(),
nn.Dropout(config.dropout_rate),
nn.Linear(hidden_dim // 2, 1),
nn.Sigmoid()
)
self.temperature = nn.Parameter(torch.ones(1))
def encode_clause(self, input_ids: torch.Tensor, attention_mask: torch.Tensor) -> torch.Tensor:
"""Encode a single clause with BERT"""
if self.bert is not None:
outputs = self.bert(input_ids=input_ids, attention_mask=attention_mask)
return outputs.pooler_output # [batch, 768]
else:
batch_size = input_ids.size(0)
return torch.randn(batch_size, self.bert_hidden_size).to(input_ids.device)
def forward_single_clause(
self,
input_ids: torch.Tensor,
attention_mask: torch.Tensor
) -> Dict[str, torch.Tensor]:
"""
Forward pass for SINGLE clause (for training compatibility)
This maintains compatibility with your current training pipeline
where clauses are processed one at a time during training.
"""
# Encode clause with BERT
clause_embedding = self.encode_clause(input_ids, attention_mask)
# Since we don't have section context during single-clause training,
# pass through LSTM with single timestep to maintain architecture
lstm_out, _ = self.clause_to_section(clause_embedding.unsqueeze(1))
context_aware_repr = lstm_out.squeeze(1) # [batch, hidden_dim*2]
# Make predictions
risk_logits = self.risk_classifier(context_aware_repr)
severity_score = self.severity_regressor(context_aware_repr).squeeze(-1) * 10
importance_score = self.importance_regressor(context_aware_repr).squeeze(-1) * 10
calibrated_logits = risk_logits / self.temperature
return {
'risk_logits': risk_logits,
'calibrated_logits': calibrated_logits,
'severity_score': severity_score,
'importance_score': importance_score,
'pooled_output': context_aware_repr
}
def forward_document(
self,
document_structure: List[List[Dict[str, torch.Tensor]]]
) -> Dict[str, Any]:
"""
Forward pass for FULL DOCUMENT (for inference with context)
Args:
document_structure: List of sections, each containing list of clause inputs
Example: [
[ # Section 1
{'input_ids': tensor, 'attention_mask': tensor},
{'input_ids': tensor, 'attention_mask': tensor}
],
[ # Section 2
{'input_ids': tensor, 'attention_mask': tensor}
]
]
Returns:
Document-level predictions with full context
"""
device = next(self.parameters()).device
section_vectors = []
all_clause_predictions = []
attention_weights = {'clause': [], 'section': None}
# Process each section
for section_idx, section_clauses in enumerate(document_structure):
if not section_clauses:
continue
# Encode all clauses in this section
clause_embeddings = []
for clause_input in section_clauses:
input_ids = clause_input['input_ids'].unsqueeze(0).to(device)
attention_mask = clause_input['attention_mask'].unsqueeze(0).to(device)
clause_emb = self.encode_clause(input_ids, attention_mask)
clause_embeddings.append(clause_emb)
# Stack: [num_clauses, 768]
clause_hidden = torch.cat(clause_embeddings, dim=0)
# LSTM over clauses β context-aware representations
clause_lstm_out, _ = self.clause_to_section(clause_hidden.unsqueeze(0))
# clause_lstm_out: [1, num_clauses, hidden_dim*2]
# Attention over clauses β section representation
attention_logits = self.clause_attention(clause_lstm_out)
clause_attn = F.softmax(attention_logits, dim=1)
section_vec = torch.sum(clause_lstm_out * clause_attn, dim=1)
section_vectors.append(section_vec)
attention_weights['clause'].append(clause_attn.squeeze(0))
# Predict for each clause using context-aware representation
for i in range(len(section_clauses)):
clause_repr = clause_lstm_out[0, i, :] # Context-aware!
risk_logits = self.risk_classifier(clause_repr)
severity = self.severity_regressor(clause_repr).squeeze() * 10
importance = self.importance_regressor(clause_repr).squeeze() * 10
calibrated_logits = risk_logits / self.temperature
all_clause_predictions.append({
'risk_logits': risk_logits,
'calibrated_logits': calibrated_logits,
'severity_score': severity,
'importance_score': importance,
'section_idx': section_idx,
'clause_idx': i
})
# Aggregate sections β document
if section_vectors:
section_hidden = torch.cat(section_vectors, dim=0)
section_lstm_out, _ = self.section_to_document(section_hidden.unsqueeze(0))
attention_logits = self.section_attention(section_lstm_out)
section_attn = F.softmax(attention_logits, dim=1)
document_vec = torch.sum(section_lstm_out * section_attn, dim=1)
attention_weights['section'] = section_attn.squeeze(0)
else:
document_vec = torch.zeros(1, self.hidden_dim * 2).to(device)
return {
'document_embedding': document_vec,
'clause_predictions': all_clause_predictions,
'attention_weights': attention_weights
}
def predict_document(
self,
document_structure: List[List[Dict[str, torch.Tensor]]]
) -> Dict[str, Any]:
"""Inference mode with formatted output"""
self.eval()
with torch.no_grad():
outputs = self.forward_document(document_structure)
# Format predictions
predictions = []
for pred in outputs['clause_predictions']:
risk_probs = F.softmax(pred['calibrated_logits'], dim=0).cpu().numpy()
predicted_risk = int(risk_probs.argmax())
predictions.append({
'section_idx': pred['section_idx'],
'clause_idx': pred['clause_idx'],
'predicted_risk_id': predicted_risk,
'risk_probabilities': risk_probs.tolist(),
'confidence': float(risk_probs[predicted_risk]),
'severity_score': pred['severity_score'].item(),
'importance_score': pred['importance_score'].item()
})
return {
'clauses': predictions,
'attention_weights': {
'clause': [attn.cpu().numpy().tolist() for attn in outputs['attention_weights']['clause']],
'section': outputs['attention_weights']['section'].cpu().numpy().tolist()
if outputs['attention_weights']['section'] is not None else None
},
'summary': {
'num_sections': len(document_structure),
'num_clauses': len(predictions),
'avg_severity': sum(p['severity_score'] for p in predictions) / len(predictions) if predictions else 0,
'high_risk_count': sum(1 for p in predictions if p['severity_score'] > 7)
}
}
# ============================================================================
# ROBERTA-BASE MODEL FOR LEGAL RISK ANALYSIS
# ============================================================================
class RoBERTaLegalBERT(nn.Module):
"""
Simplified Legal Risk Analysis Model using RoBERTa-base
**Architecture:**
RoBERTa-base (125M params) β Multi-task heads (risk, severity, importance)
**Key Features:**
- Pre-trained RoBERTa-base for better contextual understanding
- Multi-task learning: Risk classification + Severity + Importance
- Temperature scaling for calibrated confidence scores
- Focal Loss support for handling class imbalance
- Compatible with all existing training infrastructure
**Why RoBERTa over BERT:**
β
Better pre-training (10x more data, longer sequences)
β
Dynamic masking (better generalization)
β
No NSP task (focuses on MLM)
β
Byte-level BPE (better handling of legal terminology)
β
State-of-the-art performance on legal benchmarks
**Usage:**
config = LegalBertConfig(bert_model_name='roberta-base')
model = RoBERTaLegalBERT(config, num_discovered_risks=7)
# Training (single clause)
outputs = model(input_ids, attention_mask)
# Inference with predictions
predictions = model.predict_risk_pattern(input_ids, attention_mask)
"""
def __init__(self, config, num_discovered_risks: int = 7):
super().__init__()
self.config = config
self.num_discovered_risks = num_discovered_risks
# Load RoBERTa model
try:
self.roberta = AutoModel.from_pretrained(config.bert_model_name)
# Configure RoBERTa dropout
self.roberta.config.hidden_dropout_prob = config.dropout_rate
self.roberta.config.attention_probs_dropout_prob = config.dropout_rate
self.hidden_size = self.roberta.config.hidden_size # 768 for roberta-base
print(f"β
Loaded {config.bert_model_name} (hidden_size={self.hidden_size})")
except Exception as e:
print(f"β οΈ Warning: Could not load RoBERTa model: {e}")
print(" Using mock model for testing")
self.roberta = None
self.hidden_size = 768
# Multi-task prediction heads
# Head 1: Risk Classification (discovered patterns)
self.risk_classifier = nn.Sequential(
nn.Dropout(config.dropout_rate),
nn.Linear(self.hidden_size, self.hidden_size // 2),
nn.ReLU(),
nn.Dropout(config.dropout_rate),
nn.Linear(self.hidden_size // 2, num_discovered_risks)
)
# Head 2: Severity Regression (0-10 scale)
self.severity_regressor = nn.Sequential(
nn.Dropout(config.dropout_rate),
nn.Linear(self.hidden_size, self.hidden_size // 4),
nn.ReLU(),
nn.Dropout(config.dropout_rate),
nn.Linear(self.hidden_size // 4, 1),
nn.Sigmoid() # Output 0-1, will be scaled to 0-10
)
# Head 3: Importance Regression (0-10 scale)
self.importance_regressor = nn.Sequential(
nn.Dropout(config.dropout_rate),
nn.Linear(self.hidden_size, self.hidden_size // 4),
nn.ReLU(),
nn.Dropout(config.dropout_rate),
nn.Linear(self.hidden_size // 4, 1),
nn.Sigmoid() # Output 0-1, will be scaled to 0-10
)
# Temperature parameter for calibration
self.temperature = nn.Parameter(torch.ones(1))
def forward(self, input_ids: torch.Tensor, attention_mask: torch.Tensor,
output_attentions: bool = False) -> Dict[str, torch.Tensor]:
"""
Forward pass through RoBERTa and task-specific heads
Args:
input_ids: Token IDs [batch_size, seq_len]
attention_mask: Attention mask [batch_size, seq_len]
output_attentions: Whether to return attention weights
Returns:
Dictionary with:
- risk_logits: Classification logits [batch_size, num_risks]
- calibrated_logits: Temperature-scaled logits
- severity_score: Severity predictions [batch_size]
- importance_score: Importance predictions [batch_size]
- pooled_output: RoBERTa pooled representation [batch_size, 768]
- attentions: (optional) Attention weights for analysis
"""
if self.roberta is not None:
# Real RoBERTa forward pass
outputs = self.roberta(
input_ids=input_ids,
attention_mask=attention_mask,
output_attentions=output_attentions
)
# RoBERTa uses <s> token (first token) as sentence representation
pooled_output = outputs.last_hidden_state[:, 0, :] # [batch, hidden_size]
attentions = outputs.attentions if output_attentions else None
else:
# Mock output for testing
batch_size = input_ids.size(0)
pooled_output = torch.randn(batch_size, self.hidden_size, device=input_ids.device)
attentions = None
# Multi-task predictions
risk_logits = self.risk_classifier(pooled_output)
severity_score = self.severity_regressor(pooled_output).squeeze(-1) * 10 # Scale to 0-10
importance_score = self.importance_regressor(pooled_output).squeeze(-1) * 10 # Scale to 0-10
# Apply temperature scaling for calibrated probabilities
calibrated_logits = risk_logits / self.temperature
result = {
'risk_logits': risk_logits,
'calibrated_logits': calibrated_logits,
'severity_score': severity_score,
'importance_score': importance_score,
'pooled_output': pooled_output
}
if output_attentions and attentions is not None:
result['attentions'] = attentions
return result
def predict_risk_pattern(self, input_ids: torch.Tensor, attention_mask: torch.Tensor,
return_attentions: bool = False) -> Dict[str, Any]:
"""
Make predictions with interpretable outputs
Args:
input_ids: Token IDs [batch_size, seq_len]
attention_mask: Attention mask [batch_size, seq_len]
return_attentions: Whether to include attention weights
Returns:
Dictionary with predictions, probabilities, and confidence scores
"""
self.eval()
with torch.no_grad():
outputs = self.forward(input_ids, attention_mask, output_attentions=return_attentions)
# Get predictions
risk_probs = torch.softmax(outputs['calibrated_logits'], dim=-1)
predicted_risk = torch.argmax(risk_probs, dim=-1)
confidence = torch.max(risk_probs, dim=-1)[0]
result = {
'predicted_risk_id': predicted_risk.cpu().numpy(),
'risk_probabilities': risk_probs.cpu().numpy(),
'confidence': confidence.cpu().numpy(),
'severity_score': outputs['severity_score'].cpu().numpy(),
'importance_score': outputs['importance_score'].cpu().numpy()
}
if return_attentions and 'attentions' in outputs:
result['attentions'] = outputs['attentions']
return result
def analyze_attention(self, input_ids: torch.Tensor, attention_mask: torch.Tensor,
tokenizer: Optional['LegalBertTokenizer'] = None) -> Dict[str, Any]:
"""
Analyze RoBERTa attention patterns to identify important tokens
Args:
input_ids: Token IDs [batch_size, seq_len]
attention_mask: Attention mask [batch_size, seq_len]
tokenizer: Tokenizer for decoding tokens
Returns:
Dictionary with token importance scores and top tokens
"""
self.eval()
with torch.no_grad():
outputs = self.forward(input_ids, attention_mask, output_attentions=True)
if 'attentions' not in outputs or outputs['attentions'] is None:
return {'error': 'Attention weights not available'}
attentions = outputs['attentions'] # Tuple of (batch, num_heads, seq_len, seq_len)
batch_size, seq_len = input_ids.shape
# Stack all layers: (num_layers, batch, num_heads, seq_len, seq_len)
all_attentions = torch.stack(attentions)
# Get attention to <s> token (index 0) - RoBERTa's classification token
# Average across layers and heads
cls_attention = all_attentions[:, :, :, 0, :].mean(dim=[0, 2]) # (batch, seq_len)
# Get global attention (average from all tokens)
global_attention = all_attentions.mean(dim=[0, 2, 3]) # (batch, seq_len)
# Combine for final importance score
token_importance = (cls_attention + global_attention) / 2
token_importance = token_importance * attention_mask # Mask padding
# Get top-k important tokens
k = min(10, seq_len)
top_values, top_indices = torch.topk(token_importance, k, dim=1)
result = {
'token_importance': token_importance.cpu().numpy(),
'top_token_indices': top_indices.cpu().numpy(),
'top_token_scores': top_values.cpu().numpy(),
'attention_weights': {
'cls_attention': cls_attention.cpu().numpy(),
'global_attention': global_attention.cpu().numpy()
}
}
# Add layer-wise analysis
layer_attentions = []
for layer_idx, layer_attn in enumerate(attentions):
layer_cls_attn = layer_attn[:, :, 0, :].mean(dim=1) # (batch, seq_len)
layer_attentions.append({
'layer': layer_idx,
'cls_attention': layer_cls_attn.cpu().numpy()
})
result['layer_analysis'] = layer_attentions
# Decode tokens if tokenizer provided
if tokenizer is not None and tokenizer.tokenizer is not None:
tokens = tokenizer.tokenizer.convert_ids_to_tokens(input_ids[0])
top_tokens = [tokens[idx] for idx in top_indices[0].cpu().numpy()]
result['tokens'] = tokens
result['top_tokens'] = top_tokens
return result |