Welcome back! In the previous lesson, we explored the concept of multi-query expansion, which enhances search results by broadening the scope of a user's query. Today, we will delve into hybrid retrieval, a powerful technique that combines metadata and vector search to improve the accuracy and relevance of search results. This lesson will build on your existing knowledge and introduce you to the practical implementation of hybrid retrieval using ChromaDB.

Hybrid retrieval leverages the strengths of both metadata and vector search. Metadata provides structured information that can refine search queries, while vector search uses embeddings to understand the semantic meaning of text. By combining these approaches, we can achieve more precise and relevant search outcomes. Let's explore how this works in practice.

Before we dive into the implementation, let's briefly revisit the concepts of metadata and vector search. Metadata refers to structured information that describes the content of a document, such as categories, tags, or author names. It allows us to filter and refine search queries based on specific attributes.

Vector search, on the other hand, uses embeddings to capture the semantic meaning of text. By representing text as vectors, we can measure the similarity between different pieces of text, enabling us to perform semantic searches that go beyond simple keyword matching.

Combining metadata and vector search allows us to leverage the strengths of both approaches. Metadata helps us narrow down the search space, while vector search ensures that the results are semantically relevant. This synergy is what makes hybrid retrieval a powerful tool in semantic search systems.

Before we dive into the implementation of hybrid retrieval, let's set up some sample data using ChromaDB. This will help us understand how the data is structured and how it can be queried.

In this setup, we load documents from a JSON file and initialize a ChromaDB client. We create a collection named "document_collection" with an embedding function. We then add documents to the collection in batches, each with associated metadata such as title, category, tags, and date. This data will be used in our hybrid retrieval examples.

Let's walk through the process of implementing hybrid retrieval using ChromaDB. We'll use a code snippet to demonstrate how to perform a hybrid search by combining metadata and vector retrieval, especially with ambiguous queries that could belong to multiple categories.

For example, consider the query "Python". In your dataset, "Python" can refer to either the programming language (in the "Technology" category) or the snake (in the "Travel" category).

By applying different metadata filters, hybrid retrieval helps disambiguate the results and return contextually relevant documents for each category.

Here's the code:

In this example, we use the ambiguous query "Python". By applying the metadata filter for category: Technology, the search returns documents about the Python programming language. When we switch the filter to category: Travel, the search returns documents about pythons as animals in the context of wildlife and travel. This demonstrates how hybrid retrieval can resolve ambiguity and provide results that are relevant to the user's intent based on context.

Let's look at another example using a different ambiguous query, "Coach", which in your dataset can refer to either a business coach or a mode of travel (bus).

By running the same query with different metadata filters, you can observe how hybrid retrieval surfaces the most relevant documents for each context—either a business coach or coach travel—demonstrating the power and flexibility of combining metadata and vector search.

As you implement hybrid retrieval, you may encounter some common challenges. One potential issue is ensuring that the metadata filters are correctly defined and match the structure of your dataset. It's important to verify that the metadata fields used in the where clause exist in your data.

Another challenge is optimizing the balance between metadata and vector search. Depending on your dataset and search requirements, you may need to adjust the weight given to each component to achieve the best results.

If you encounter any issues, double-check your code for syntax errors and ensure that your environment is set up correctly. With practice, you'll become more comfortable troubleshooting and resolving these challenges.

In this lesson, we explored the concept of hybrid retrieval and its role in enhancing search accuracy by combining metadata and vector search. We implemented a hybrid search using ChromaDB and demonstrated how to execute queries that leverage both metadata and semantic understanding.

As you move on to the practice exercises, focus on applying what you've learned about hybrid retrieval. Experiment with different queries and metadata filters to see how they affect the search results. Mastering hybrid retrieval will provide a strong foundation for more advanced search techniques in future lessons. Keep up the great work, and I look forward to seeing your progress!