In XML terminology, what is the component that defines the structure (allowed elements, attributes, order, and occurrence) of an XML document?

Introduction / Context:
XML relies on separate schema or DTD artifacts to define valid document structure. This question asks you to identify the component responsible for that structural definition.

Given Data / Assumptions:

• We want the artifact that declares elements, attributes, and content models.
• We are considering classic DTD usage.

Concept / Approach:
A DTD (Document Type Definition) declares the allowable building blocks of an XML document. The DOCTYPE declaration in an XML file references or embeds a DTD, but the DTD itself is the structure definition.

Step-by-Step Solution:

Verification / Alternative check:
Looking at a DTD file shows ELEMENT and ATTLIST declarations that define permissible structure.

Why Other Options Are Wrong:

• DOCTYPE: the declaration that references a DTD, not the definition itself.
• #PCDATA: a token used inside DTDs to indicate parsed character data.
• HTML Stylesheet: unrelated to XML structure definition.

Common Pitfalls:
Using “DOCTYPE” and “DTD” interchangeably; DOCTYPE is the declaration, DTD is the schema-like definition.

Final Answer:
DTD