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XML Documents Overview: The Panoramic PerspectiveBog'liq Ceponkus, Hoodbhoy - Applied XML - Toolkit for ProgrammersXML Documents Overview: The Panoramic Perspective
At the most basic level, XML documents are made of at least one—though usually
many—
entities
. An entity is a flexible information storage unit. Until parsed, XML files are
really just text files, so essentially every XML document is an entity (XML documents can
be made up of many other entities too). However, entities can also be non-XML related.
Any binary file (for example picture, sound, video, or database) can be an entity too.
In levels of abstraction, a document is at the highest level (also called
root level
) and is
referred to as the
document entity
. An XML parser reads a document entity and follows
all references contained therein to piece together the complete document.
Entities that are made of XML syntax contain two parts, the content (raw information, also
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called character data) and the XML markup. We briefly touched on what markup was in
Chapter 1
. Markup is information about content that helps us use the content. In XML, the
actual markup serves several purposes:
•
It provides a fairly simple and standardized syntax that XML parsers can use for
resolving the information it describes.
•
The markup provides a rich method of describing the hierarchical structure of the
content by breaking the content information (character data) into chunks called
elements
that in turn are further described by
attributes
. The hierarchical structure of
the entire document is described through the usage of markup.
An XML document can be roughly broken down into three generic sections of markup
collections:
•
Prolog
•
Document Type Definition (optional)
•
Root Element
Each of these sections is further broken down into more detailed structures. Figure 3.2
shows all of these generic markup sections with their subsections. We go into some
detail about all of these in this chapter.
Figure 3.2:
Putting XML documents in perspective: The Panoramic Perspective.
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