Question

Distinguish between internal dtd and external dtd

Answer 1

Answer:

The only difference between internal and external is in the way it's declared with DOCTYPE. Internal DTD : You can write rules inside XML document using declaration. External DTD : You can write rules in a separate file (with .dtd extension).

Answer 2

DTD declarations either internal XML document or make external DTD file, after linked to a XML document.
Internal DTD : You can write rules inside XML document using declaration. Scope of this DTD within this document. Advantages is document validated by itself without external reference.
External DTD : You can write rules in a separate file (with .dtd extension). later this file linked to a XML document. This way you can linked several XML documents refer same DTD rules.