What is the difference between XML and XSD?

Question

What is the difference between Extensible Markup Language (XML) and XML Schema (XSD)?

Answer 1

XML has a much wider application than f.ex. HTML. It doesn't have an intrinsic, or default "application". So, while you might not really care that web pages are also governed by what's allowed, from the author's side, you'll probably want to precisely define what an XML document may and may not contain.

It's like designing a database.

The thing about XML technologies is that they are textual in nature. With XSD, it means you have a data structure definition framework that can be "plugged in" to text processing tools like PHP. So not only can you manipulate the data itself, but also very easily change and document the structure, and even auto-generate front-ends.

Viewed like this, XSD is the "glue" or "middleware" between data (XML) and data-processing tools.