XML

eXtensible Markup Language

  • About

    Differences from HTML

    • XML elements must have a closing tag
    • XML tags are case sensitive
    • All XML elements must be properly nested
    • All XML documents must have a root tag. The first tag in an XML document is the root tag.
    • Attribute values must always be quoted With XML, it is illegal to omit quotation marks around attribute values

     


    Rules in creating XML tags

    Naming elements

    • can contain letters, numbers, and other characters
    • Names must not start with a number or punctuation character
    • Names must not start with the letters xml (or XML or Xml ..)
    • Names cannot contain spaces
    • The ":" should not be used in element names because it is reserved to be used for something called namespaces

    Attributes

    • Attribute values must always be enclosed in quotes, but either single or double quotes can be used.
    • Data can be stored in child elements or in attributes. Take a look at these examples:

      <person sex="male">
           <name> Allen Grewe </name>
      </person>

      OR

      <person>
           <sex>male</sex>
           <name>Allen Grewe</name>
      </person>



      Here are some of the problems using attributes:

      • attributes cannot contain multiple values (child elements can)
      • attributes are not easily expandable (for future changes)
      • attributes cannot describe structures (child elements can)
      • attributes are more difficult to manipulate by program code


      One Good use for Attributes:

      • to use as IDs. These ID references can be used to access XML elements in much the same way as the NAME or ID attributes in HTML.





    Example

    <?xml version="1.0" encoding="ISO-8859-1">

    <note>
    <to>Butch</to>
    <from>Allen</from>
    <heading>Play time</heading>

    <body>I will be returning from campus and hope to find you well. </body>

    </note>
    viewing code
    The first line in the document - the XML declaration - defines the XML version and the character encoding used in the document. In this case the document conforms to the 1.0 specification of XML and uses the ISO-8859-1 (Latin-1/West European) character set.


    The next line describes the root element of the document (like it was saying: "this document is a note"):

    The next 4 lines describe 4 child elements of the root (to, from, heading, and body)

 

Whats going on???

Since XML tags are "made up" or "invented" by the author of the XML document, we cannot know if a tag like <table> describes a HTML type of table, or if it describes a wooden kitchen table. Without any information about how to display the data, most browsers will just display the XML document as it is.

To specify display properties:

To Specify the XML tags:

  • You need a DTD or an XML schema|

    There are other possibilities being explored:

    • RELAX Regular Language description for XML
    • SOX Schema for Object-oriented XML
    • Schematron Schema for Object-oriented XML

 

Data Binding???

Data Islands can be bound to HTML elements (like HTML tables). In the example below, an XML Data Island with an ID "cdcat" is loaded from an external XML file. An HTML table is bound to the Data Island with a data source attribute, and finally the tabledata elements are bound to the XML data with a data field attribute inside a span.

(works on only some browsers)

<html>
<body>

<xml id="cdcat" src="cd_catalog.xml"> </xml>

<table border="1" datasrc="#cdcat">
<tr>
<td><span datafld="ARTIST"></span></td>
<td><span datafld="TITLE"></span></td>
</tr>
</table>

</body>
</html>

see it working
cd_catalog.xml file

 

 

Applications

VoiceXML, More VoiceXML

XMLSoap
© Lynne Grewe