XML Notes

Definition
- Extensible Markup Language used as a complement to HTML
- Designed to structure, store and send data
- No predefined tags, you must define your tags!
- Stored in plain text files
Use

Used to store data in files external to the HTML page
Used to store data inside HTML pages as data islands
Used to exchange data between incompatable systems
Used to share data
Used to create new languages ie: WML tutorial
excludes the need for data conversion between applications

Example

          <?xml version = "1.0" encoding = "ISO-8859-1"?>
          <NOTE>
            <TO>bill</TO>
            <FROM>bob</FROM>
            <HEADING>Reminder</HEADING>
            <BODY>Don't forget me this weekend!</BODY>
          </NOTE>

The first line is always the XML declaration
The second line describes the root element of the document
The next 4 lines describe child elements of the root
The last line defines the end of the root element

Syntax

All 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 element

All child elements must be within this root element
Attribute values must always be quoted
White space is not truncated
A new line is always stored as LF

Elements

XML elements are extensible, so you can add onto them later
XML elements have relationships as parents and children
XML elements have simple naming rules
Elements have content
Element content
Mixed content
Simple or text content
Empty content
Element names can contain letters, numbers and other characters
Element names must not start with a number or punctuation character
Element names must not start with the letters XML, xml or Xml
Element names cannot contain spaces

Attributes

XML elements can have attributes in the start tag like HTML
Attributes often provide information that is not part of the data
Attributes can use either single or double quotes
if the attributes encloses a double quoted item... use single quotes
<gangster name = 'George "Shotgun" Zeigler'>

if the attributes encloses a single quoted item... use double quotes
<gangster name = "George 'Shotgun' Zeigler">

Data can be stored in child elements or in attributes
Attributes cannot contain multiple values, child elements can
Attributes are not easily expandable
Attributes cannot describe structures, child elements can
Attributes are more difficult to manipulate by program code
Attribute values are not easy to validate in a document type definition

Validation
- XML validated against a DTD is Valid XML
- Well formed XML documents have correct syntax and conform to a DTD
- A DTD defines the legal elements of an XML document
- XML Schema is an XML based alternative to DTD
- Validation errors will halt the XML processing program
Browsers

I.E. Supports
- Viewing of XML documents
- Full support for W3C DTD standards
- XML embedded in HTML as data islands
- Binding XML data to HTML elements
- Transforming and displaying XML with XSL
- Displaying XML with CSS
- Access to the XML DOM
I.E. also has support for Behaviors
- Behaviors is a Microsoft only technology
- Behaviors can separate scripts from an HTML page
- Behaviors can store XML data on the client's disk

Viewing XML Files

Open it with I.E.
Browser will report errors
XML documents do not carry information specifying display

Displaying XML with CSS

With CSS you can add display information to an XML document
<?xml-stylesheet type = "text/css" href="simple.css"?>
Use XHTML to create XML pages

Displaying XML with XSL: Extensible Style Sheet Language

XSL is the preferred style sheet language of XML
<?xml-stylesheet type = "text/xsl" href="simple.xsl">
Links the XML file to the XSL file

Data Islands

XML data can be embedded in HTML using the <XML> tag
Example:

<XML Id = "note">
  <to>Bob</to>
  <from>Bill</from>
  <heading>Reminder</heading>
  <body>Don't forget me this weekend!</body>
</note>
</XML>
Data islands can also be bound to HTML elements
They automatically load so no JavaScript or VBScript needed

Example:

</table>

Artist	Title
This is my CD collection

The Microsoft XML Parser

Needed to read, update, create and manipulate an XML document during run
Using the XML parser that comes with I.E.
The parser is available to scripts both inside HTML documents and
inside ASP files. The parser features a language-neutral programming
model that supports:
- JavaScript, VBScript, Perl, VB, Java, C++ and more
- W3C XML 1.0 and XML DOM
- DTD and validation
JavaScript
var xmlDoc=new ActiveXObject("Microsoft.XMLDOM")
VBScript
set xmlDoc=CreateObject("Microsoft.XMLDOM")
VBScript in ASP
set xmldoc=Server.CreateObject("Microsoft.XMLDOM")

Loading an XML file into the parser
XML files can be loaded into the XML parser using script code

Example:
<SCRIPT type="text/javascript">
  var xmlDoc = new ActiveXObject("Microsoft.XMLDOM")
  xmlDoc.async="false"
  xmlDoc.load("Example 4.xml")
  // -------- processing the document goes here
</SCRIPT>

Loading Pure XML Text Into The Parser
XML text can also be loaded from a text string

Example:
<SCRIPT type="text/javascript">
  var text="<note>"
  text = text+"<to>Bob</to><from>Bill</from>"
  text = text+"<heding>Reminder</heding>"
  text = text+"<body>Don't forget me this weekend!</body>"
  text = text+"</note>"
  var xmlDoc = new ActiveXObject("Microsoft.XMLDOM")
  xmlDoc.async="false"
  xmlDoc.loadXML(text)
  // ------- processing goes here
</SCRIPT>

Displaying XML with JavaScript/VBScript
Both can be used to import data from an XML file and display it in HTML

Example:
    XML Data         HTML Page

Example:
    XML Data         HTML Page

More...

XML In Real Life

The XML standard makes it easier to produce, receive and archive information across different hardware, software and programming languages.

NameSpaces

Provides a method to avoid element name conflicts
Don't use HTML element names!
Use a prefix

<H:TABLE>

Use a namespace attribute in the start tag of an element

<H:TABLE XMLNS:H="/Files/XML/Work Out/Schedule"

Syntax

xmlns:namespace-prefix="namespace"

The namespace should be a URI (Uniform Resource Identifier)

All child elements with the same prefix are associated with the namespace

The address used to identify the namespace is not used by the parser to look up information. The only purpose is to give the namespace a unique name however, very often companies use the namespace as a pointer to a web site containing information about the namespace.

Uniform Resource Identifiers

(URI) A string of characters which identifies an internet resource.
(URL) Identifies an internet domain address
(URN) Universal Resource Name

Default Namespaces

Defining a default namespace for an element saves having to use prefixes in the child elements

<ELEMENT XMLNS="NameSpace">

CDATA

Everything inside a CDATA section is ignored by the parser

A CDATA section starts with "<![CDATA]" and ends with "]]>":

Example:

<![CDATA[

function matchwo(a,b)

{

if (a < b && a < 0) then

{

return 1

}

else

{

return 0

}

]]>

</SCRIPT>

A CDATA section cannot contain another CDATA section

Illegal XML characters have to be replaced by entity references

<MESSAGE>if salary < 100000 then</MESSAGE>

5 predefined entity references in XML

<	<	less than
>	>	greater than
&	&	ampersand
'	'	apostrophe
"	"	quotation mark

Make sure there are no spaces or line breaks inside the "]]>" string

Encoding

XML documents can contain foreign characters so save XML documents as Unicode
Watch out for encoding errors!

Servers

XML files can be generated on an internet server without any installed XML controls
XML files can be stored on the server same way as HTML files
XML can be generated on an ASP server without any installed XML software

ASP file
<#
response.ContentType="text/xml"

response.Write("<?xml version = '1.0' encoding='ISO-8859-1'?>")
response.Write("<note>")
respnose.Write("<from>Bob</from>")
response.Write("<to>Bill</to>")
response.Write("<message>Remember me this weekend</message>")
response.Write("</note>")
#>

XML can be generated from a database without any installed XML software

ASP file
<#
response.ContentType = "text/sml"

set conn=Server.CreateObject("ADODB.Connection")
conn.provider="Microsoft.Jet.OLEDB.4.0'"
conn.open server.mappath("../ado/database.mdb")
sql="select fname,lname from tblGuestBook"
set rs=Conn.Execute(sql)

rs.MoveFirst()

response.write("<?xml version='1.0' encoding='ISO-8859-1'?>")
response.write("<guestbook>")
while (not rs.EOF)
  response.write("<guest>")
  response.write("<fname>" & rs("fname") & "</fname>")
  response.write("<lname>" & rs("lname") & "</lname>")
  response.write("</guest>")
  rs.MoveNext()
wend

rs.close()
conn.close
response.write("</guestbook>")
#>

Applications

Start with an XML document

Example 3.xml

Load the document into a Data Island on a page

Bind the Data Island to an HTML table

<THEAD>

<TH>Title</TH>

<TH>Artist</TH>

</THEAD>

</TR>

</TABLE>

Title	Artist	Year

<SPAN> or <DIV> elements can also be used to display XML data

Adding a Navigation Script to the XML

function MoveNext()

{

x=xmldso.recordset

if (x.absoluteposition < x.recordcount)

{

x.movenext()

}

function moveprevious()

{

x=xmldso.recordset

if (x.absolutposition > 1)

{

x.moveprevious()

}

</SCRIPT>

HTTP Requests using JavaScript or VBScript

XML data can be requested from a server using an HTTP request

var objHTTP = new ActiveXObject("Microsoft.XMLHTTP")
objHTTP.Open('GET','httprequest.asp',false)
ObjHTTP.Send()

To view the above result

document.all['A1'].innerText=objHTTP.status
document.all['A2'].innerText=objHTTP.statusText
document.all['A3'].innerText=objHTTP.responseText

With HTTP Requests you communicate with the Server See Example 5

Behaviors

A Behavior is a CSS Attribute Selector that can point to an XML file
that contains code to be executed against elements in a web page
A <STYLE> Method to completely remove script code from an HTML page
Allows for script libraries and attaching to elements on multiple HTML pages
A Microsoft only technology
File extension = ".htc"
Example:

<STYLE> H1 ( Behavior:URL(Behave.htc) )</STYLE>

The Behavior code for the Attribute is stored in an XML document Behave.htc

<component>
  <attach for="element event="onmouseover" handler="hig_lite" />
  <attach for="element event="onmouseout" handler="low_lite" />
  <script type="text/javascript">
    function hig_lite()
    {
      element.style.color=255
    }
    function low_lite()
    {
      element.style.color=0
    }
  </script>
</component>

Related Technologies

XHTML - Extensible HTML
XHTML is the reformulation of HTML 4.01 in XML.
CSS - Cascading Style sheets
CSS style sheets can be added to XML document to provide display information
XSL - Extensible Style Sheet Language

XSL consists of 3 parts

XSLT - XML document transformation

Used to transform XML files into many different output formats

XPath - a pattern matching syntax

A language for addressing parts of an XML document
Designed to be used by XSLT and XPointer

A formatting Object Interpretation

XLink - XML Linking Language

Allows elements to be inserted into XML to create links between XML resources

XPointer - XML Pointer Language

Supports addressing into the internal structures of XML documents
such as; elements, attributes and content

DTD - Document Type Definition

Can be used to define the legal building blocks of an XML document

NameSpaces

Defines a method for defining element and attribute names
used in XML by associating them with URI references

XSD - XML Schema

Powerful alternatives to DTD's written in XML

XDR - XML Data Reduced

A reduced version of XML Schema

DOM - Document Object Model

Defines interfaces, properties and methods to manipulate XML documents

XQL - XML Query Language

Supports query facilities to extract data from XML documents

SAX - Simple API for XML

Interface to read and maniuplate XML documents

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