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Getting Started
 Contents 
One Line Index Creation
Walkthrough
Getting Started#
LangChain primarily focuses on constructing indexes with the goal of using them as a Retriever. In order to best understand what this means, it’s worth highlighting what the base Retriever interface is. The BaseRetriever class in LangChain is as follows:
from abc import ABC, abstractmethod
from typing import List
from langchain.schema import Document
class BaseRetriever(ABC):
    @abstractmethod
    def get_relevant_documents(self, query: str) -> List[Document]:
        """Get texts relevant for a query.
        Args:
            query: string to find relevant texts for
        Returns:
            List of relevant documents
        """
It’s that simple! The get_relevant_documents method can be implemented however you see fit.
Of course, we also help construct what we think useful Retrievers are. The main type of Retriever that we focus on is a Vectorstore retriever. We will focus on that for the rest of this guide.
In order to understand what a vectorstore retriever is, it’s important to understand what a Vectorstore is. So let’s look at that.
By default, LangChain uses Chroma as the vectorstore to index and search embeddings. To walk through this tutorial, we’ll first need to install chromadb.
pip install chromadb
This example showcases question answering over documents.
We have chosen this as the example for getting started because it nicely combines a lot of different elements (Text splitters, embeddings, vectorstores) and then also shows how to use them in a chain.
Question answering over documents consists of four steps:
Create an index
Create a Retriever from that index
Create a question answering chain
Ask questions!
rtdocs_stable/api.python.langchain.com/en/stable/modules/indexes/getting_started.html