XML Schema Definition (XSD) files are used to define the structure and data types of an XML document. They ensure that the XML document adheres to a specific structure by defining the allowed elements, attributes, and their data types, thereby enforcing a consistent format.
Option A is correct because XSD files define the elements, attributes, and structure (hierarchy) of an XML document.
Option D is correct because XSD files provide a standardized format, ensuring that all parties working with the XML document use the same set of tags and structure.
Option B (Every XML document must have an XSD file defined for it) is incorrect; not every XML document requires an XSD file, although it's beneficial for validation.
Option C (An XSD file is not an XML document) is incorrect because XSD files themselves are written in XML.
Supporting Reference:
W3C XML Schema Definition (XSD) Documentation: Explains the purpose and structure of XSD files, including their role in defining XML document schemas.