Schema-First

Schema-first extraction is an approach to document processing where you define the output structure — every field, its type, its validation rules — before writing a single line of extraction logic. The schema is the specification. It describes exactly what a successful extraction looks like: which fields are required, which are optional, what format dates should be in, what range is valid for numeric values. Extraction logic is then written to satisfy that specification.

Most PDF extraction projects start with the document. You open a PDF, look at the text, write a regex, extract a value. Repeat for each field. This works for one document type with one layout. It doesn’t scale. Schema-first extraction inverts the order: define exactly what the output should look like before you write a single line of extraction code. The schema becomes the specification that every extraction function has to satisfy — and the tool that tells you, immediately and explicitly, when an extraction fails.