Tutorial: Embedding Metadata for Improved Retrieval


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Last Updated: April 25, 2024

This tutorial uses Haystack 2.0. To learn more, read the Haystack 2.0 announcement or visit the Haystack 2.0 Documentation.

⚠️ Note of caution: The method showcased in this tutorial is not always the right approach for all types of metadata. This method works best when the embedded metadata is meaningful. For example, here we’re showcasing embedding the “title” meta field, which can also provide good context for the embedding model.

Overview

While indexing documents into a document store, we have 2 options: embed the text for that document or embed the text alongside some meaningful metadata. In some cases, embedding meaningful metadata alongside the contents of a document may improve retrieval down the line.

In this tutorial, we will see how we can embed metadata as well as the text of a document. We will fetch various pages from Wikipedia and index them into an InMemoryDocumentStore with metadata information that includes their title, and URL. Next, we will see how retrieval with and without this metadata.

Setup

Prepare the Colab Environment

Install Haystack

Install Haystack 2.0 and other required packages with pip:

%%bash

pip install haystack-ai wikipedia sentence-transformers

Enable Telemetry

Knowing you’re using this tutorial helps us decide where to invest our efforts to build a better product but you can always opt out by commenting the following line. See Telemetry for more details.

from haystack.telemetry import tutorial_running

tutorial_running(39)

Indexing Documents with Metadata

Create a pipeline to store the small example dataset in the InMemoryDocumentStore with their embeddings. We will use SentenceTransformersDocumentEmbedder to generate embeddings for your Documents and write them to the document store with the DocumentWriter.

After adding these components to your pipeline, connect them and run the pipeline.

💡 The InMemoryDocumentStore is the simplest document store to run tutorials with and comes with no additional requirements. This can be changed to any of the other available document stores such as Weaviate, AstraDB, Qdrant, Pinecone and more. Check out the full list of document stores with instructions on how to run them.

First, we’ll create a helper function that can create indexing pipelines. We will optionally provide this function with meta_fields_to_embed. If provided, the SentenceTransformersDocumentEmbedder will be initialized with metadata to embed alongside the content of the document.

For example, the embedder below will be embedding the “url” field as well as the contents of documents:

from haystack.components.embedders import SentenceTransformersTextEmbedder

embedder = SentenceTransformersDocumentEmbedder(meta_fields_to_embed=["url"])

from haystack import Pipeline
from haystack.components.preprocessors import DocumentCleaner, DocumentSplitter
from haystack.components.embedders import SentenceTransformersDocumentEmbedder
from haystack.components.writers import DocumentWriter
from haystack.document_stores.types import DuplicatePolicy
from haystack.utils import ComponentDevice


def create_indexing_pipeline(document_store, metadata_fields_to_embed=None):
    document_cleaner = DocumentCleaner()
    document_splitter = DocumentSplitter(split_by="sentence", split_length=2)
    document_embedder = SentenceTransformersDocumentEmbedder(
        model="thenlper/gte-large", meta_fields_to_embed=metadata_fields_to_embed
    )
    document_writer = DocumentWriter(document_store=document_store, policy=DuplicatePolicy.OVERWRITE)

    indexing_pipeline = Pipeline()
    indexing_pipeline.add_component("cleaner", document_cleaner)
    indexing_pipeline.add_component("splitter", document_splitter)
    indexing_pipeline.add_component("embedder", document_embedder)
    indexing_pipeline.add_component("writer", document_writer)

    indexing_pipeline.connect("cleaner", "splitter")
    indexing_pipeline.connect("splitter", "embedder")
    indexing_pipeline.connect("embedder", "writer")

    return indexing_pipeline

Next, we can index our documents from various wikipedia articles. We will create 2 indexing pipelines:

  • The indexing_pipeline: which indexes only the contents of the documents. We will index these documents into document_store.
  • The indexing_with_metadata_pipeline: which indexes meta fields alongside the contents of the documents. We will index these documents into document_store_with_embedded_metadata.
import wikipedia
from haystack import Document
from haystack.document_stores.in_memory import InMemoryDocumentStore

some_bands = """The Beatles,The Cure""".split(",")

raw_docs = []

for title in some_bands:
    page = wikipedia.page(title=title, auto_suggest=False)
    doc = Document(content=page.content, meta={"title": page.title, "url": page.url})
    raw_docs.append(doc)

document_store = InMemoryDocumentStore(embedding_similarity_function="cosine")
document_store_with_embedded_metadata = InMemoryDocumentStore(embedding_similarity_function="cosine")

indexing_pipeline = create_indexing_pipeline(document_store=document_store)
indexing_with_metadata_pipeline = create_indexing_pipeline(
    document_store=document_store_with_embedded_metadata, metadata_fields_to_embed=["title"]
)

indexing_pipeline.run({"cleaner": {"documents": raw_docs}})
indexing_with_metadata_pipeline.run({"cleaner": {"documents": raw_docs}})

Comparing Retrieval With and Without Embedded Metadata

As a final step, we will be creating a retrieval pipeline that will have 2 retrievers:

  • First: retrieving from the document_store, where we have not embedded metadata.
  • Second: retrieving from the document_store_with_embedded_metadata, where we have embedded metadata.

We will then be able to compare the results and see if embedding metadata has helped with retrieval in this case.

💡 Here, we are using the InMemoryEmbeddintRetriever because we used the InMemoryDocumentStore above. If you’re using another document store, change this to use the accompanying embedding retriever for the document store you are using. Check out the Embedders Documentation for a full list

from haystack.components.embedders import SentenceTransformersTextEmbedder
from haystack.components.retrievers.in_memory import InMemoryEmbeddingRetriever

retrieval_pipeline = Pipeline()
retrieval_pipeline.add_component("text_embedder", SentenceTransformersTextEmbedder(model="thenlper/gte-large"))
retrieval_pipeline.add_component(
    "retriever", InMemoryEmbeddingRetriever(document_store=document_store, scale_score=False, top_k=3)
)
retrieval_pipeline.add_component(
    "retriever_with_embeddings",
    InMemoryEmbeddingRetriever(document_store=document_store_with_embedded_metadata, scale_score=False, top_k=3),
)

retrieval_pipeline.connect("text_embedder", "retriever")
retrieval_pipeline.connect("text_embedder", "retriever_with_embeddings")

Let’s run the pipeline and compare the results from retriever and retirever_with_embeddings. Below you’ll see 3 documents returned by each retriever, ranked by relevance.

Notice that with the question “Have the Beatles ever been to Bangor?”, the first pipeline is not returning relevant documents, but the second one is. Here, the meta field “title” is helpful, because as it turns out, the document that contains the information about The Beatles visiting Bangor does not contain a reference to “The Beatles”. But, by embedding metadata, the embedding model is able to retrieve the right document.

result = retrieval_pipeline.run({"text_embedder": {"text": "Have the Beatles ever been to Bangor?"}})

print("Retriever Results:\n")
for doc in result["retriever"]["documents"]:
    print(doc)

print("Retriever with Embeddings Results:\n")
for doc in result["retriever_with_embeddings"]["documents"]:
    print(doc)

What’s next

🎉 Congratulations! You’ve embedded metadata while indexing, to improve the results of retrieval!

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Thanks for reading!