Introduction to XML
• XML stands for Extensible Markup Language. Because it is
extensible, XML has been used to create a wide variety of
different markup vocabularies.
1
CML: An XML Example
2
GolfML: Another XML Example
<?xml version="1.0" encoding="utf-8"?>
<golfml xmlns="http://pga.com/golfml">
<course name=“The Oaks”>
<tee num=“1”>
<par>5</par>
<handicap>15</handicap>
<length units=“yds”>475</length>
</tee>
<tee num=“2”>
…
</tee>
</course>
</golfml>
3
Why is XML Important?
• XML gives us a way to create and maintain structured
documents in plain text that can be rendered in a variety of
different ways.
• A primary objective of XML is to completely separate content
from presentation.
Example: The Asbury Park Press is a structured document
containing pages, columns, etc.
The news is just plain text (including the images).
Newspapers can be rendered on paper or online.
4
Where XML Fits into
Other Markup Languages
5
DTDs and XML Documents
• A DTD (Document Type Definition) or schema
specifies the rules for what a legal XML document
may contain.
• An XML document is well-formed if it contains no
syntax errors and fulfills all of the specifications for
XML code as defined by the W3C.
• An XML document is valid if it is well-formed and also
satisfies the rules laid out in the DTD or schema
attached to the document.
6
The Structure of an XML Document: The Prolog
• The XML declaration is always the first line of code in an XML
document. It tells the parser what follows is written using XML.
• The complete syntax is:
<?xml version=“version number”
encoding=“encoding type” standalone=“yes | no” ?>
• The typical declaration is:
<?xml version=“1.0” encoding=“UTF-8”
standalone = “yes” ?>
7
The Structure of an XML Document: Elements
•
•
•
•
•
•
Closed elements have the following syntax:
<element_name>Content</element_name>
For example: <Artist>Miles Davis</Artist>
Open elements have the syntax: <element />
For example: <Jazz_Music />
Element names are case sensitive, must begin with a letter (or _), and may
not contain spaces.
Elements can be (properly) nested. For example:
<playlist>
<track>So What</track>
<track>Blue in Green</track>
</playlist>
All elements must be nested within a single root element.
Comments are enclosed in <!-- comment --> (like HTML).
8
The Structure of an XML Document: Attributes
• An attribute is a property of an element. They are text strings
placed in single or double quotes. The syntax is:
<element_name attribute=“value”>
9
The Element Hierarchy
10
Special Character References
Special symbols can be inserted into an XML document
using either the character reference or entity reference,
11
CDATA Sections
• Validators can get confused by some XML:
<temperatureRange>
> 100 degrees
</temperatureRange>
• You must separate the file into PCDATA and CDATA.
• Parsed character data (PCDATA) is text to be parsed by a browser or parser
(all the XML code: declarations, elements, attributes, comments).
• Unparsed character data (CDATA) is text not to be processed by the browser
or parser. A CDATA section marks a block of text as CDATA so that parsers
ignore any text within it:
<temperatureRange>
<![CDATA[
> 100 degrees
]]>
</temperatureRange>
12
Mark Your XML with the Sections
You Don’t Want Parsed
CDATA
section
13
Parsing an XML Document
14
Displaying an XML Document in a Web Browser
If it’s well-formed
If it’s not well-formed
15
Linking to a Style Sheet
16
Applying Styles to the XML Elements
• To apply a style sheet to a document, use the syntax:
selector {attribute1:value1; attribute2:value2; …}
For example: artist
{color:red; font-weight:bold}
17
Linking the XML to the Style Sheet
•The link from the XML document to a style sheet is created
using a processing statement. A processing instruction is a
command that gives instructions to the XML parser.
18
The XML Document Formatted with the Style Sheet
19