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Vector Databases: Pinecone, Weaviate & pgvector · Lesson

Semantic Search & Hybrid Search

Implement advanced search techniques combining vector similarity with keyword matching for superior results.

Semantic Search & Hybrid Search is a free Vector Databases: Pinecone, Weaviate & pgvector lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Vector Databases: Pinecone, Weaviate & pgvector learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Beyond Basic Searches

Welcome! In this lesson, we'll dive into advanced search techniques in Weaviate. Moving past simple vector searches, we'll explore how to combine different methods for incredibly precise results.

We'll cover:

  • Pure semantic search
  • Traditional keyword (BM25) search
  • The power of hybrid search

Semantic Search: Meaning First

Semantic search finds items based on their meaning, not just exact words. It uses vector embeddings to represent data, measuring "distance" to find similar concepts. Weaviate uses .with_near_text() for this.

Try this example:

import weaviate
import os

# Connect to your Weaviate instance
# Ensure WEAVIATE_URL is set (e.g., "http://localhost:8080")
client = weaviate.Client(
    url=os.getenv("WEAVIATE_URL", "http://localhost:8080")
)

# Make sure you have an 'Article' class with 'title' and 'content' properties
# and some data imported for this to work!

query_concept = "latest advancements in technology"

response = client.query.get(
    "Article", # Your class name
    ["title", "content"]
).with_near_text(
    {"concepts": [query_concept]}
).with_limit(2).do()

print("Semantic Search Results:")
for item in response["data"]["Get"]["Article"]:
    print(f"- {item['title']}")

Keyword Search Fundamentals

While semantic search is powerful, sometimes you need to find exact keywords. This is where traditional keyword search comes in. Weaviate supports this using the BM25 algorithm.

BM25 (Best Match 25) is a ranking function used by search engines to estimate the relevance of documents to a given search query. It's great for precision when you know exactly what words you're looking for.

Keyword Search with BM25

You can perform keyword searches in Weaviate by combining a .with_where() filter with a text search, and asking for the _additional {score} to see BM25 relevance.

Here's how to search for articles containing specific keywords:

import weaviate
import os

# Connect to your Weaviate instance
client = weaviate.Client(
    url=os.getenv("WEAVIATE_URL", "http://localhost:8080")
)

# Make sure you have an 'Article' class with 'title' and 'content' properties
# and some data imported for this to work!

keyword_query = "AI" # Search for articles containing "AI"

response = client.query.get(
    "Article",
    ["title", "content", "_additional {score}"] # Request BM25 score
).with_where({
    "path": ["content"], # Search in the 'content' field
    "operator": "Like",
    "valueText": f"*{keyword_query}*" # Wildcard search
}).with_limit(2).do()

print("Keyword Search Results:")
for item in response["data"]["Get"]["Article"]:
    print(f"- {item['title']} (BM25 Score: {item['_additional']['score']:.2f})")

Why Hybrid? Limitations

Both semantic and keyword searches have strengths and weaknesses:

  • Semantic: Great for conceptual understanding, but can miss exact terms.
  • Keyword: Excellent for exact matches, but struggles with synonyms or nuanced meaning.

Imagine searching for "best car for family trips." Semantic search might show SUVs, while keyword search might only show articles with "family" and "trip." What if you want both?

Introducing Hybrid Search

Hybrid search combines the strengths of semantic (vector) search and keyword (BM25) search. It retrieves results based on both conceptual similarity and exact term matching, then intelligently fuses them.

This leads to more comprehensive and relevant results, especially for complex or ambiguous queries.

Weaviate's `with_hybrid`

Hybrid search combines semantic and keyword strengths. Weaviate's .with_hybrid() operator makes this easy. It takes both a query and an alpha parameter to control the blend:

  • alpha = 0: Pure keyword
  • alpha = 1: Pure semantic
  • alpha = 0.5: Equal blend (default)

Experiment with this:

import weaviate
import os

# Connect to your Weaviate instance
client = weaviate.Client(
    url=os.getenv("WEAVIATE_URL", "http://localhost:8080")
)

# Make sure you have an 'Article' class with 'title' and 'content' properties
# and some data imported for this to work!

query = "AI tools for data analysis" # Hybrid query text
alpha_value = 0.7 # 0.7 for more semantic weighting

response = client.query.get(
    "Article",
    ["title", "content", "_additional {score, id}"] # Request score & ID
).with_hybrid(
    query=query,
    alpha=alpha_value
).with_limit(3).do()

print(f"Hybrid Search Results (alpha={alpha_value}):")
for item in response["data"]["Get"]["Article"]:
    # The 'score' here is the hybrid score
    print(f"- {item['title']} (Score: {item['_additional']['score']:.2f})")

Understanding Result Fusion (RRF)

When you perform a hybrid search, Weaviate needs a way to combine the rankings from both the semantic and keyword searches into a single, unified list. This is often done using an algorithm like Reciprocal Rank Fusion (RRF).

RRF is a clever method that assigns a score to each document based on its rank in the individual search results. Documents that rank highly in both semantic and keyword searches will get a significantly boosted final score.

Benefits of Hybrid Search

Hybrid search offers several advantages:

  • Improved Relevance: Catches both exact matches and conceptually similar items.
  • Robustness: Performs well even with short, ambiguous, or rare queries.
  • User Satisfaction: Leads to more comprehensive and helpful search results.

It's a crucial technique for building advanced search experiences in AI applications.

Test Your Knowledge

Hybrid search combines semantic and keyword search. Which parameter in Weaviate's .with_hybrid() operator controls the balance between these two search types?

Summary of Advanced Search

Great job! You've mastered advanced search techniques in Weaviate. We explored:

  • Semantic Search: Based on meaning and vector similarity.
  • Keyword Search: Using BM25 for exact term matching.
  • Hybrid Search: Combining both for superior relevance, controlled by the alpha parameter.

These powerful tools will help you build more intelligent and robust search applications. Keep experimenting with different query types and alpha values!

Frequently asked questions

Is the “Semantic Search & Hybrid Search” lesson free?

Yes — the full text of “Semantic Search & Hybrid Search” is free to read here on the web, and the Vector Databases: Pinecone, Weaviate & pgvector course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Vector Databases: Pinecone, Weaviate & pgvector course, upgrade to CoddyKit PRO.

What will I learn in “Semantic Search & Hybrid Search”?

Implement advanced search techniques combining vector similarity with keyword matching for superior results. You practise Vector Databases: Pinecone, Weaviate & pgvector with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Vector Databases: Pinecone, Weaviate & pgvector?

No prior experience is required. Vector Databases: Pinecone, Weaviate & pgvector on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Semantic Search & Hybrid Search” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Vector Databases: Pinecone, Weaviate & pgvector lesson?

Yes. Every Vector Databases: Pinecone, Weaviate & pgvector lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Semantic Search & Hybrid Search
  2. Using Weaviate Modules
  3. Backup and Restore Strategies
  4. Multi-Tenancy in Weaviate
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