What type of documents include invoices and receipts?

Invoices and receipts are categorized as semi-structured documents because they contain a mix of both structured and unstructured data. Semi-structured documents have a predefined format that allows certain elements to be easily identified and extracted, such as dates, amounts, and item descriptions, while also including free text that may vary in content and structure.

For invoices and receipts, there is typically a consistent layout and specific fields where crucial data is placed, such as vendor information and itemized lists of purchases, which makes it easier to parse out the structured parts. However, there is still variability in how other information might be presented or phrased, which is characteristic of unstructured data.

This classification contrasts with purely structured documents, which have a strict schema (like databases), and unstructured documents, which lack any inherent structure (like emails or free-form text files). Digital documents refer to any type of document existing in digital form, but this term doesn't specifically address the format or structure of the data contained within.