XML Document Structure
March 29, 1999
Physically, documents are composed of a set of
"entities"
that are identified by unique names, (except the document
entity that we will discuss later). All documents begin
with a "root" or document entity. All other entities are
optional.
So as not to confuse you, I want to mention that you have
not seen any entities in previous examples. We have only
needed to rely on the "document entity" which you don't need
to explicitly define because XML gives it to you for free.
We'll look at entities in greater detail later.
What is important for the moment is that you understand that
entities can be thought of as aliases for more complex
functions. That is, a single entity name can take the place
of a whole lot of text. As in any computer aliasing scheme,
entity references cut down on the amount of typing you have to
do because anytime you need to reference that bunch of text,
you simply use the alias name and the processor will expand
out the contents of the alias for you.
As opposed to physical structure, XML documents have a logical
structure as well. Logically, documents are composed of
declarations,
elements,
comments,
character references, and
processing instructions, all of which are indicated in the
document by explicit markup.
Additional Resources:
The Well-Formed Document
Introduction to XML For Web Developers | Table of Contents
Data Versus Markup
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