Question: The ______ file defines the structure of the XML document.

Answer:

The "Document Type Definition" (DTD) file or the "XML Schema Definition" (XSD) file defines the structure of an XML document. Both DTD and XSD are commonly used to specify the rules and constraints for the elements, attributes, and relationships within an XML document. They define the allowed elements, their hierarchy, data types, and any additional restrictions or requirements. By referencing the DTD or XSD file, the XML document can be validated against the defined structure to ensure its adherence to the specified rules.