Hybrid search (semantic + keyword) in Prompt Engineering / GenAI - Model Pipeline Trace

Model Pipeline - Hybrid search (semantic + keyword)

This hybrid search pipeline combines keyword matching with semantic understanding to find the most relevant documents. It first filters documents by keywords, then ranks them by semantic similarity using a trained model.

Data Flow - 5 Stages

1Input Query

1 query string→User inputs a search query→1 query string

"best Italian restaurants near me"

↓

2Keyword Filtering

N documents x text→Filter documents containing query keywords→M documents x text (M ≤ N)

From 1000 docs, filter to 150 docs containing words like 'Italian', 'restaurants'

↓

3Semantic Embedding

1 query string and M documents x text→Convert query and documents to vector embeddings→1 query vector (768 dims), M document vectors (768 dims each)

Query vector: [0.12, -0.05, ..., 0.33], Document vector: [0.10, -0.02, ..., 0.30]

↓

4Similarity Scoring

1 query vector, M document vectors→Calculate cosine similarity between query and each document vector→M similarity scores (float between -1 and 1)

[0.85, 0.78, 0.65, ...]

↓

5Ranking and Output

M documents with similarity scores→Sort documents by similarity score descending→Top K documents ranked

Top 5 documents with scores: [(doc23, 0.85), (doc7, 0.83), ...]

Training Trace - Epoch by Epoch

Loss
0.7 |****
0.6 |*** 
0.5 |**  
0.4 |*   
0.3 |*   
0.2 |    
     1 2 3 4 5 Epochs

Epoch	Loss ↓	Accuracy ↑	Observation
1	0.65	0.60	Model starts learning semantic relations, initial moderate accuracy
2	0.48	0.72	Loss decreases, accuracy improves as embeddings better capture meaning
3	0.35	0.81	Model converges, semantic similarity scores become more reliable
4	0.30	0.85	Fine tuning improves ranking quality, loss stabilizes
5	0.28	0.87	Final epoch shows best balance of loss and accuracy

Prediction Trace - 4 Layers

Layer 1: Keyword Filtering

Layer 2: Semantic Embedding

Layer 3: Similarity Scoring

Layer 4: Ranking

Model Quiz - 3 Questions

What is the main purpose of the keyword filtering stage?

A To reduce the number of documents before semantic comparison

B To convert text into vectors

C To calculate similarity scores

D To rank documents by relevance

Key Insight

Combining keyword filtering with semantic similarity balances speed and understanding, enabling efficient and meaningful search results.

Practice

1. What is the main advantage of hybrid search combining semantic and keyword methods?

easy

A. It improves search relevance by using both exact words and meaning.

B. It only uses exact keyword matching for faster results.

C. It ignores word meanings to focus on keyword frequency.

D. It replaces keywords with random words for variety.

Solution

1. Step 1: Understand keyword and semantic search roles

   Keyword search finds exact word matches; semantic search finds meaning matches.

2. Step 2: Combine both for better results

   Hybrid search uses both to improve relevance and user satisfaction.

3. Final Answer:

   It improves search relevance by using both exact words and meaning. -> Option A

4. Quick Check:

   Hybrid search = better relevance [OK]

Hint: Hybrid = exact words + meaning for best results [OK]

Common Mistakes:

• Thinking hybrid search uses only keywords
• Assuming semantic search ignores keywords
• Believing hybrid search slows down search always

2. Which of the following is the correct way to combine semantic and keyword scores in hybrid search?

easy

A. final_score = semantic_score * keyword_score

B. final_score = semantic_score / keyword_score

C. final_score = semantic_score - keyword_score

D. final_score = semantic_score + keyword_score

Solution

1. Step 1: Understand score combination methods

   Adding scores balances contributions from both semantic and keyword parts.

2. Step 2: Choose addition for hybrid scoring

   Adding semantic and keyword scores is common to combine relevance signals.

3. Final Answer:

   final_score = semantic_score + keyword_score -> Option D

4. Quick Check:

   Hybrid score = sum of semantic and keyword [OK]

Hint: Add scores to combine semantic and keyword relevance [OK]

Common Mistakes:

• Multiplying scores causing very small or large values
• Subtracting scores losing positive relevance
• Dividing scores causing errors if denominator is zero

3. Given the code snippet:

semantic_scores = [0.8, 0.5, 0.3]
keyword_scores = [0.6, 0.7, 0.4]
final_scores = [s + k for s, k in zip(semantic_scores, keyword_scores)]
print(final_scores)

What is the output?

medium

A. [1.4, 1.2, 0.7]

B. [0.2, -0.2, -0.1]

C. [0.48, 0.35, 0.12]

D. [1.2, 1.4, 0.7]

Solution

1. Step 1: Add corresponding semantic and keyword scores

   0.8+0.6=1.4, 0.5+0.7=1.2, 0.3+0.4=0.7

2. Step 2: Create list of summed scores

   final_scores = [1.4, 1.2, 0.7]

3. Final Answer:

   [1.4, 1.2, 0.7] -> Option A

4. Quick Check:

   Sum pairs = [1.4, 1.2, 0.7] [OK]

Hint: Add pairs element-wise for final scores [OK]

Common Mistakes:

• Multiplying instead of adding scores
• Mixing order of scores in zip
• Confusing subtraction with addition

4. Identify the error in this hybrid search scoring code:

semantic_scores = [0.9, 0.4, 0.7]
keyword_scores = [0.5, 0.6]
final_scores = [s + k for s, k in zip(semantic_scores, keyword_scores)]
print(final_scores)

medium

A. Adding scores should use multiplication instead.

B. Using zip causes a syntax error here.

C. Lists have different lengths causing missing scores.

D. The print statement is missing parentheses.

Solution

1. Step 1: Check list lengths

   semantic_scores has 3 items; keyword_scores has 2 items.

2. Step 2: Understand zip behavior

   zip stops at shortest list length, so last semantic score is ignored.

3. Final Answer:

   Lists have different lengths causing missing scores. -> Option C

4. Quick Check:

   Unequal list lengths truncate results [OK]

Hint: Ensure lists are same length before zipping [OK]

Common Mistakes:

• Assuming zip pads shorter list automatically
• Thinking zip causes syntax error
• Believing multiplication is required for hybrid scores

5. You want to improve a hybrid search system by weighting semantic similarity twice as much as keyword matching. Which formula correctly applies this?

hard

A. final_score = semantic_score + 2 * keyword_score

B. final_score = 2 * semantic_score + keyword_score

C. final_score = semantic_score * keyword_score * 2

D. final_score = (semantic_score + keyword_score) / 2

Solution

1. Step 1: Identify weighting requirement

   Semantic similarity should count double compared to keyword score.

2. Step 2: Apply weights in formula

   Multiply semantic_score by 2, then add keyword_score.

3. Final Answer:

   final_score = 2 * semantic_score + keyword_score -> Option B

4. Quick Check:

   Semantic weighted double = 2 * semantic + keyword [OK]

Hint: Multiply semantic score by 2 before adding keyword [OK]

Common Mistakes:

• Weighting keyword score instead of semantic
• Multiplying all scores together
• Dividing sum instead of weighting