Flash CS3 Documentation
|Programming ActionScript 3.0 > Working with XML > Basics of XML|
XML is a standard way of representing structured information so that it is easy for computers to work with and reasonably easy for people to write and understand. XML is an abbreviation for eXtensible Markup Language. The XML standard is available at www.w3.org/XML/.
XML offers a standard and convenient way to categorize data, to make it easier to read, access, and manipulate. XML uses a tree structure and tag structure that is similar to HTML. Here is a simple example of XML data:
<song> <title>What you know?</title> <artist>Steve and the flubberblubs</artist> <year>1989</year> <lastplayed>2006-10-17-08:31</lastplayed> </song>
XML data can also be more complex, with tags nested in other tags as well as attributes and other structural components. Here is a more complex example of XML data:
<album> <title>Questions, unanswered</title> <artist>Steve and the flubberblubs</artist> <year>1989</year> <tracks> <song tracknumber="1" length="4:05"> <title>What do you know?</title> <artist>Steve and the flubberblubs</artist> <lastplayed>2006-10-17-08:31</lastplayed> </song> <song tracknumber="2" length="3:45"> <title>Who do you know?</title> <artist>Steve and the flubberblubs</artist> <lastplayed>2006-10-17-08:35</lastplayed> </song> <song tracknumber="3" length="5:14"> <title>When do you know?</title> <artist>Steve and the flubberblubs</artist> <lastplayed>2006-10-17-08:39</lastplayed> </song> <song tracknumber="4" length="4:19"> <title>Do you know?</title> <artist>Steve and the flubberblubs</artist> <lastplayed>2006-10-17-08:44</lastplayed> </song> </tracks> </album>
Notice that this XML document contains other complete XML structures within it (such as the
ong tags with their children). It also demonstrates other XML structures such as attributes (
length in the
ong tags), and tags that contain other tags rather than containing data (such as the
If you have little or no experience with XML, here is a brief description of the most common aspects of XML data. XML data is written in plain-text form, with a specific syntax for organizing the information into a structured format. Generally, a single set of XML data is known as an XML document. In XML format, data is organized into elements (which can be single data items or containers for other elements) using a hierarchical structure. Every XML document has a single element as the top level or main item; inside this root element there may be a single piece of information, although there are more likely to be other elements, which in turn contain other elements, and so forth. For example, this XML document contains the information about a music album:
<song tracknumber="1" length="4:05"> <title>What do you know?</title> <artist>Steve and the flubberblubs</artist> <mood>Happy</mood> <lastplayed>2006-10-17-08:31</lastplayed> </song>
Each element is distinguished by a set of tags--the element's name wrapped in angle brackets (less-than and greater-than signs). The opening tag, indicating the start of the element, has the element name:
The closing tag, which marks the end of the element, has a forward slash before the element's name:
If an element contains no content, it can be written as an empty element (sometimes called a self-closing element). In XML, this element:
is identical to this element:
In addition to the element's content contained between the opening and closing tags, an element can also include other values, known as attributes, defined in the element's opening tag. For example, this XML element defines a single attribute named
length, with the value
Each XML element has content, which is either a single value, one or more XML elements, or nothing (for an empty element).
To learn more about working with XML, there are a number of additional books and resources for learning more about XML, including these web sites:
ActionScript 3.0 includes several classes that are used for working with XML-structured information. The two main classes are as follows:
<artist type="composer">Fred Wilson</artist> <artist type="conductor">James Schmidt</artist> <artist type="soloist">Susan Harriet Thurndon</artist>
For more advanced uses involving XML namespaces, ActionScript also includes the Namespace and QName classes. For more information, see Using XML namespaces.
In addition to the built-in classes for working with XML, ActionScript 3.0 also includes several operators that provide specific functionality for accessing and manipulating XML data. This approach to working with XML using these classes and operators is known as ECMAScript for XML (E4X), as defined by the ECMA-357 edition 2 specification.
When you work with XML in ActionScript, you are likely to do the following tasks:
The following reference list contains important terms used in this chapter:
attributename="value"format, rather than being written as a separate child element nested inside the element.
As you're working through the chapter, you may want to test some of the example code listings for yourself. Essentially all the code listings in this chapter already include the appropriate
trace() function call. To test the code listings in this chapter:
You will see the results of the
trace() function in the Output panel.
This and other techniques for testing example code listings are described in more detail in Testing in-chapter example code listings.
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