Enhancing Document Extraction with Azure AI Document Intelligence and LangChain for RAG Workflows.

Overview.

The broadening of conventional data engineering pipelines and applications to include document extraction and preprocessing for unstructured PDFs, audio, and video files is becoming more prevalent. This shift is propelled by the increasing demand for advanced generative AI applications in businesses, adhering to the RAG (Retrievable Augmented Generation) model. In this post, I will discuss a proof of concept that utilizes Azure AI Document Intelligence to augment these functionalities.

 

In a prior solution, I examined the capability of Azure AI Search to automatically vectorize data through its integrated vectorization feature. This feature manages the entire pipeline process, from ingestion and extraction to enrichment and uploading data to the search index, with minimal or no custom coding required. Nonetheless, I noted a limitation: the current skills, despite the option to import external ones, failed to extract all vital content from documents, such as embedded tables.

 

Introduction.

In this post and the accompanying notebook, I present a solution utilizing the prebuilt layout model from Azure AI Document Intelligence to extract essential content (including a table) from a PDF document. Subsequently, it employs the semantic chunking feature rather than the fixed-length chunking option. This approach aims to address the limitations of the prior solution that could not "crack" the embedded table in the PDF document, enhancing the relevance and precision of search retrieval.

 

This is the first of two posts, which shows a solution that uses Azure AI Document Intelligence and LangChain to create a Retrieval Augmented Generation (RAG) workflow. It uses the LangChain Azure AI Document Intelligence document loader to ingest, extract and retrieve tables values, paragraphs, and layout information from a PDF file. The output is in markdown format, which is processed by LangChain's markdown header splitter. This class supports the semantic chunking feature of Azure AI Document Intelligence service to produce contextually aware chunks of the source document.

 

We employ the Azure AI Search Python SDK to build the Azure AI Search index, load the semantically chunked documents into this index content field and execute a hybrid + semantic search query at the end of the notebook to assess the search result relevance.

 

Below is a straightforward architectural diagram of the solution:

 

 

Before this post extends too much and loses its appeal, let's explore the essential elements of the solution architecture and the corresponding notebook code implementation that are pertinent to this discussion.

 

LangChain - Ingestion, Extraction and Semantic Chunking:

LangChain is a framework for developing LLM (large language model) powered applications. LangChain has built a huge collection of abstractions that enable the integration of LLMs to external data sources, user input query and other components and services required to build GenAI application use cases. We introduced LangChain into this solution because it provided two key abstractions:

 

1. The Azure AI Document Intelligence Loader API offers an interface for loading data into Azure AI Document Intelligence and extracting the necessary content from documents. In this proof of concept, I am utilizing a PDF document that contains an embedded table. To facilitate the successful import of the PDF document from Azure Blob Storage, the RBAC role of Storage Blob Data Reader has been granted to the Document Intelligence managed identity for the Blob storage resource.

The 'prebuilt layout' extraction model for Document Intelligence is one of the parameter values provided during the ingestion task. It supports formatting of tables with column headers into key-value pairs (to enhance readability for the LLM), and each table row is transformed into a text line, while maintaining the original structure of the table values.

 

2. The MarkdownHeaderTextSplitter class divides the markdown file generated from an extracted PDF document according to specified headers. Since a markdown file is structured with headers, this organizes the content into semantic sections. The headers used for splitting are determined by the 'headers_to_split_on' configuration.

 

Chunking is a crucial component in the development of any RAG-based solution. There are two primary methods of chunking: fixed-sized and semantic. This PoC aims to evaluate the relevance and accuracy of RAG responses using the semantic chunking method. This technique divides extracted content according to specific content headers or sections, as opposed to the fixed-sized method, which relies on an overlap configuration to preserve contextual relevance across text segments. Semantic chunking allows an application to identify semantically coherent fragments within sentences or paragraphs. These fragments can be processed separately and then reassembled into semantic representations without losing information, context, or semantic integrity. The text's inherent meaning guides the chunking process. In any document extraction process, the chunking strategy requires careful consideration and planning, as it significantly impacts the relevance and accuracy of query responses in RAG-based solutions. Determining the size of tokens per page can aid in the implementation of chunking.

 

The text splitter's output is a list of document objects, as demonstrated in the following code snippet from the notebook.:

 

 

Azure AI Search - Create and Load Vector Index:

Azure AI Search offers secure and rapid information retrieval at scale for data content within generative AI applications. In this scenario, the content of the PDF document, which is chunked, will be vectorized and stored in the search service to enable the millisecond retrieval times necessary for RAG-based applications. Such quick retrieval cannot be achieved using Azure Blob storage. The search service does not interact with the primary data store of blob storage, except when utilizing an Indexer.

 

I utilized the Azure AI Search Python SDK to construct the vector search index by first defining the schema, then initiating the data import process. For the vector search configuration, I chose the Hierarchical Navigable Small World (HNSW) algorithm over the Exhaustive k-nearest neighbors (KNN) because it's more efficient. HNSW offers a scalable solution for nearest neighbor searches by quickly identifying approximate nearest neighbors, which is ideal for large-scale and high-dimensional data applications. Additional details on vector search configuration can be found here.

 

I am utilizing the Azure OpenAI text-embedding-ada-002 model to vectorize segmented content for vector search capabilities. An ID field for each document in the index is generated using a custom function that employs the base64 Python package. The code snippet below illustrates the configuration of the vector index and the data loading process for this proof of concept:

 

 

 

 

Azure AI Document Intelligence:

Azure AI Document Intelligence is a cloud-based Azure AI Service that enables the building of intelligent document processing solutions. In a previous exploration, I implemented the Azure AI Search integrated vectorization feature that enables an automated solution for data extraction, ingestion and retrieval for RAG applications. While it's great for a lot of use cases, I wasn't able to get answers to queries that required searching through embedded table data in the PDF file. Azure AI Document Intelligence has a wider range of document extraction models, with a lot more functionality for complex PDF documents and other file types. Two primary reasons for choosing this service:

 

1. The prebuilt layout model has the functionality to "crack" and extract data from most complex PDF documents. I directly ingested the PDF document from the Blob storage container.
2. The semantic chunking technique seems an exciting option that could potentially yield better answers and search responses than the fixed-sized chunking technique.

Semantic and Hybrid Search:

This search feature provided an accurate answer to my query regarding the health plan's cost. The prior solution failed to address this question as the extraction skills applied, along with the underlying model, were unable to completely decipher the PDF document and extract the values from the embedded table.

 

Azure Functions - Semantic Kernel:

Azure Functions, a serverless computing service, hosts the semantic kernel and LangChain source code for the application. The semantic kernel, similar to LangChain, is an LLM framework that aids in the development of Generative AI applications. In a follow-up post, I will demonstrate how I utilized the Semantic Kernel to orchestrate the various components of the Generative AI application, integrating prompts, chat services, embeddings, and native functions (plugins), among others.

 

 

Conclusion:

This post showcases how to utilize Azure AI Document Intelligence to manually process a PDF document with its prebuilt layout model and extract all the content, including any embedded tables. The objective is to employ this content to ground the responses of an LLM within a knowledgebase Q&A agent.

 

Azure AI Document Intelligence is recommended for production use cases involving a variety of complex file types and formats like PDFs. It appears to be better suited to meet application requirements compared to the Azure AI Search integrated vectorization option. Additionally, I plan to explore the evaluation of generative AI applications using the prompt flow Python SDK, responsible prompt engineering tools and techniques, and content safety measures in Azure.

The code for the PoC is available in the following repository.