The INFER_SCHEMA function is a powerful tool in the Snowflake ingestion toolkit, specifically designed to bridge the gap between semi-structured data and relational tables. In modern data engineering, files like Parquet, Avro, and ORC are "self-describing," meaning they contain their own schema definitions (field names and data types) within the file header.

Before INFER_SCHEMA existed, a Data Analyst had to manually inspect a Parquet file, identify the keys, determine their data types, and then manually write a CREATE TABLE statement with the matching columns. INFER_SCHEMA automates this by scanning a set of files in a stage and returning a result set that describes the detected schema. This allows for the dynamic creation of tables that perfectly match the incoming data files.

Evaluating the Options:

Option A is incorrect because "unstructured data" (like PDFs or Images) does not have a schema that can be "inferred" in a relational sense.

Option C is incorrect because INFER_SCHEMA operates on files in a Stage, not on data already sitting in a table cell. To parse JSON in a table, you would use functions like FLATTEN or simple path notation.

Option D is incorrect because the DESCRIBE TABLE or GET_DDL commands are used to retrieve definitions for existing tables.

Option B is the Correct answer. It specifically identifies the role of the function: detecting metadata (schema) from staged semi-structured files. This function is often used in conjunction with GENERATE_COLUMN_DESCRIPTION and CREATE TABLE ... USING TEMPLATE to fully automate the schema evolution and ingestion process.