Introduction To Xml
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Introduction to XML XML was designed to describe data and to focus on what data is. HTML was designed to display data and to focus on how data looks.
What You Should Already Know Before you continue you should have a basic understanding of the following: • •
HTML / XHTML JavaScript or VBScript
What is XML? • • • • • • •
XML stands for EXtensible Markup Language XML is a markup language much like HTML XML was designed to describe data XML tags are not predefined. You must define your own tags XML uses a Document Type Definition (DTD) or an XML Schema to describe the data XML with a DTD or XML Schema is designed to be selfdescriptive XML is a W3C Recommendation
XML is a W3C Recommendation The Extensible Markup Language (XML) became a W3C Recommendation 10. February 1998.
The Main Difference between XML and HTML XML was designed to carry data. XML is not a replacement for HTML. XML and HTML were designed with different goals: XML was designed to describe data and to focus on what data is. HTML was designed to display data and to focus on how data looks.
HTML is about displaying information, while XML is about describing information.
XML Does not DO Anything XML was not designed to DO anything. Maybe it is a little hard to understand, but XML does not DO anything. XML was created to structure, store and to send information. The following example is a note to Tove from Jani, stored as XML: <note>Tove Jani Reminder Don't forget me this weekend!
The note has a header and a message body. It also has sender and receiver information. But still, this XML document does not DO anything. It is just pure information wrapped in XML tags. Someone must write a piece of software to send, receive or display it.
XML is Free and Extensible XML tags are not predefined. You must "invent" your own tags. The tags used to mark up HTML documents and the structure of HTML documents are predefined. The author of HTML documents can only use tags that are defined in the HTML standard (like, etc.). XML allows the author to define his own tags and his own document structure. The tags in the example above (like
What You Should Already Know Before you continue you should have a basic understanding of the following: • •
HTML / XHTML JavaScript or VBScript
What is XML? • • • • • • •
XML stands for EXtensible Markup Language XML is a markup language much like HTML XML was designed to describe data XML tags are not predefined. You must define your own tags XML uses a Document Type Definition (DTD) or an XML Schema to describe the data XML with a DTD or XML Schema is designed to be selfdescriptive XML is a W3C Recommendation
XML is a W3C Recommendation The Extensible Markup Language (XML) became a W3C Recommendation 10. February 1998.
The Main Difference between XML and HTML XML was designed to carry data. XML is not a replacement for HTML. XML and HTML were designed with different goals: XML was designed to describe data and to focus on what data is. HTML was designed to display data and to focus on how data looks.
HTML is about displaying information, while XML is about describing information.
XML Does not DO Anything XML was not designed to DO anything. Maybe it is a little hard to understand, but XML does not DO anything. XML was created to structure, store and to send information. The following example is a note to Tove from Jani, stored as XML: <note>
The note has a header and a message body. It also has sender and receiver information. But still, this XML document does not DO anything. It is just pure information wrapped in XML tags. Someone must write a piece of software to send, receive or display it.
XML is Free and Extensible XML tags are not predefined. You must "invent" your own tags. The tags used to mark up HTML documents and the structure of HTML documents are predefined. The author of HTML documents can only use tags that are defined in the HTML standard (like
,
, etc.). XML allows the author to define his own tags and his own document structure. The tags in the example above (like and ) are not defined in any XML standard. These tags are "invented" by the author of the XML document.
XML is a Complement to HTML XML is not a replacement for HTML. It is important to understand that XML is not a replacement for HTML. In future Web development it is most likely that XML will be used to describe the data, while HTML will be used to format and display the same data. My best description of XML is this: XML is a crossplatform, software and hardware independent tool for transmitting information.
XML in Future Web Development XML is going to be everywhere. We have been participating in XML development since its creation. It has been amazing to see how quickly the XML standard has been developed and how quickly a large number of software vendors have adopted the standard. We strongly believe that XML will be as important to the future of the Web as HTML has been to the foundation of the Web and that XML will be the most common tool for all data manipulation and data transmission.
How can XML be Used? It is important to understand that XML was designed to store, carry, and exchange data. XML was not designed to display data.
XML can Separate Data from HTML With XML, your data is stored outside your HTML. When HTML is used to display data, the data is stored inside your HTML. With XML, data can be stored in separate XML files. This way you can concentrate on using HTML for data layout and display, and be sure that changes in the underlying data will not require any changes to your HTML. XML data can also be stored inside HTML pages as "Data Islands". You can still concentrate on using HTML only for formatting and displaying the data.
XML is Used to Exchange Data With XML, data can be exchanged between incompatible systems. In the real world, computer systems and databases contain data in incompatible formats. One of the most time consuming challenges for developers has been to exchange data between such systems over the Internet. Converting the data to XML can greatly reduce this complexity and create data that can be read by many different types of applications.
XML and B2B With XML, financial information can be exchanged over the Internet.
Expect to see a lot about XML and B2B (Business To Business) in the near future. XML is going to be the main language for exchanging financial information between businesses over the Internet. A lot of interesting B2B applications are under development.
XML Can be Used to Share Data With XML, plain text files can be used to share data. Since XML data is stored in plain text format, XML provides a software and hardwareindependent way of sharing data. This makes it much easier to create data that different applications can work with. It also makes it easier to expand or upgrade a system to new operating systems, servers, applications, and new browsers.
XML Can be Used to Store Data With XML, plain text files can be used to store data. XML can also be used to store data in files or in databases. Applications can be written to store and retrieve information from the store, and generic applications can be used to display the data.
XML Can Make your Data More Useful With XML, your data is available to more users. Since XML is independent of hardware, software and application, you can make your data available to other than only standard HTML browsers. Other clients and applications can access your XML files as data sources, like they are accessing databases. Your data can be made available to all kinds of "reading machines" (agents), and it is easier to make your data available for blind people, or people with other disabilities.
XML Can be Used to Create New Languages XML is the mother of WAP and WML.
If Developers Have Sense If they DO have sense, all future applications will exchange their data in XML. The future might give us word processors, spreadsheet applications and databases that can read each other's data in a pure text format, without any conversion utilities in between. We can only pray that Microsoft and all the other software vendors will agree.
XML Syntax Rules The syntax rules of XML are very simple and very strict. The rules are very easy to learn, and very easy to use. Because of this, creating software that can read and manipulate XML is very easy.
An Example XML Document XML documents use a selfdescribing and simple syntax. <note> Tove Jani Reminder Don't forget me this weekend!
<note>
The next 4 lines describe 4 child elements of the root (to, from, heading, and body): Tove Jani Reminder Don't forget me this weekend!
And finally the last line defines the end of the root element:
Can you detect from this example that the XML document contains a Note to Tove from Jani? Don't you agree that XML is pretty selfdescriptive?
All XML Elements Must Have a Closing Tag With XML, it is illegal to omit the closing tag. In HTML some elements do not have to have a closing tag. The following code is legal in HTML: This is a paragraph
This is another paragraph
In XML all elements must have a closing tag, like this:
This is a paragraph
This is another paragraph
Note: You might have noticed from the previous example that the XML declaration did not have a closing tag. This is not an error. The declaration is not a part of the XML document itself. It is not an XML element, and it should not have a closing tag.
XML Tags are Case Sensitive Unlike HTML, XML tags are case sensitive. With XML, the tag is different from the tag . Opening and closing tags must therefore be written with the same case: <Message>This is incorrect <message>This is correct
XML Elements Must be Properly Nested Improper nesting of tags makes no sense to XML.
In HTML some elements can be improperly nested within each other like this: This text is bold and italic
In XML all elements must be properly nested within each other like this: This text is bold and italic
XML Documents Must Have a Root Element All XML documents must contain a single tag pair to define a root element. All other elements must be within this root element. All elements can have sub elements (child elements). Sub elements must be correctly nested within their parent element: <subchild>.....
XML Attribute Values Must be Quoted With XML, it is illegal to omit quotation marks around attribute values. XML elements can have attributes in name/value pairs just like in HTML. In XML the attribute value must always be quoted. Study the two XML documents below. The first one is incorrect, the second is correct: <note date=12/11/2002> Tove Jani
<note date="12/11/2002"> Tove Jani
This is correct: date="12/11/2002". This is incorrect: date=12/11/2002.
With XML, White Space is Preserved With XML, the white space in your document is not truncated. This is unlike HTML. With HTML, a sentence like this: Hello my name is Tove, will be displayed like this: Hello my name is Tove, because HTML reduces multiple, consecutive white space characters to a single white space.
With XML, CR / LF is Converted to LF With XML, a new line is always stored as LF. Do you know what a typewriter is? Well, a typewriter is a mechanical device which was used last century to produce printed documents. :) After you have typed one line of text on a typewriter, you have to manually return the printing carriage to the left margin position and manually feed the paper up one line. In Windows applications, a new line is normally stored as a pair of characters: carriage return (CR) and line feed (LF). The character pair bears some resemblance to the typewriter actions of setting a new line. In Unix applications, a new line is normally stored as a LF character. Macintosh applications use only a CR character to store a new line.
Comments in XML The syntax for writing comments in XML is similar to that of HTML.
XML Elements XML Elements are extensible and they have relationships. XML Elements have simple naming rules.
XML Elements are Extensible XML documents can be extended to carry more information. Look at the following XML NOTE example: <note> Tove Jani Don't forget me this weekend!
Let's imagine that we created an application that extracted the , , and elements from the XML document to produce this output: To: Tove From: Jani Don't forget me this weekend! Imagine that the author of the XML document added some extra information to it:
<note> 20020801 Tove Jani Reminder Don't forget me this weekend!
Should the application break or crash? No. The application should still be able to find the , , and elements in the XML document and produce the same output. XML documents are Extensible.
XML Elements have Relationships Elements are related as parents and children. To understand XML terminology, you have to know how relationships between XML elements are named, and how element content is described. Imagine that this is a description of a book: My First XML Introduction to XML • •
What is HTML What is XML
XML Syntax •
Elements must have a closing tag
•
Elements must be properly nested
Imagine that this XML document describes the book:
My First XML <prod id="33657" media="paper"> Introduction to XML <para>What is HTML <para>What is XML XML Syntax <para>Elements must have a closing tag <para>Elements must be properly nested
Book is the root element. Title, prod, and chapter are child elements of book. Book is the parent element of title, prod, and chapter. Title, prod, and chapter are siblings (or sister elements) because they have the same parent.
Elements have Content Elements can have different content types. An XML element is everything from (including) the element's start tag to (including) the element's end tag. An element can have element content, mixed content, simple content, or empty content. An element can also have attributes. In the example above, book has element content, because it contains other elements. Chapter has mixed content because it contains both text and other elements. Para has simple content (or text content) because it contains only text. Prod has empty content, because it carries no information. In the example above only the prod element has attributes. The attribute named id has the value "33657". The attribute named media has the value "paper".
Element Naming XML elements must follow these naming rules: • • • •
Names 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, etc) Names cannot contain spaces
Take care when you "invent" element names and follow these simple rules:
separator are nice. Examples: , . Avoid "" and "." in names. For example, if you name something "firstname," it could be a mess if your software tries to subtract name from first. Or if you name something "first.name," your software may think that "name" is a property of the object "first." Element names can be as long as you like, but don't exaggerate. Names should be short and simple, like this: not like this: . XML documents often have a corresponding database, in which fields exist corresponding to elements in the XML document. A good practice is to use the naming rules of your database for the elements in the XML documents. NonEnglish letters like éòá are perfectly legal in XML element names, but watch out for problems if your software vendor doesn't support them. The ":" should not be used in element names because it is reserved to be used for something called namespaces (more later).
XML Attributes XML elements can have attributes in the start tag, just like HTML. Attributes are used to provide additional information about elements.
XML Attributes XML elements can have attributes. From HTML you will remember this: . The SRC attribute provides additional information about the IMG element. In HTML (and in XML) attributes provide additional information about elements:
Attributes often provide information that is not a part of the data. In the example below, the file type is irrelevant to the data, but important to the software that wants to manipulate the element: computer.gif
Quote Styles, "female" or 'female'?
Note: If the attribute value itself contains double quotes it is necessary to use single quotes, like in this example:
Note: If the attribute value itself contains single quotes it is necessary to use double quotes, like in this example:
Use of Elements vs. Attributes Data can be stored in child elements or in attributes. Take a look at these examples: Anna Smith
<sex>female Anna Smith
In the first example sex is an attribute. In the last, sex is a child element. Both examples provide the same information. There are no rules about when to use attributes, and when to use child elements. My experience is that attributes are handy in HTML, but in XML you should try to avoid them. Use child elements if the information feels like data.
My Favorite Way I like to store data in child elements.
<note date="12/11/2002"> Tove Jani Reminder Don't forget me this weekend!
A date element is used in the second example: <note> 12/11/2002 Tove Jani Reminder Don't forget me this weekend!
An expanded date element is used in the third: (THIS IS MY FAVORITE): <note> 12 <month>11 2002 Tove Jani Reminder Don't forget me this weekend!
• • • • •
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 attribute values are not easy to test against a Document Type Definition (DTD) which is used to define the legal elements of an XML document
If you use attributes as containers for data, you end up with documents that are difficult to read and maintain. Try to use elements to describe data. Use attributes only to provide information that is not relevant to the data. Don't end up like this (this is not how XML should be used): <note day="12" month="11" year="2002" body="Don't forget me this weekend!">
An Exception to my Attribute Rule Rules always have exceptions. My rule about attributes has one exception: Sometimes I assign ID references to elements. These ID references can be used to access XML elements in much the same way as the NAME or ID attributes in HTML. This example demonstrates this: <messages> <note id="p501"> Tove Jani Reminder Don't forget me this weekend! <note id="p502"> Jani Tove Re: Reminder I will not!
The ID in these examples is just a counter, or a unique identifier, to identify the different notes in the XML file, and not a part of the note data. What I am trying to say here is that metadata (data about data) should be stored as attributes, and that data itself should be stored as elements.
XML Validation XML with correct syntax is Well Formed XML. XML validated against a DTD is Valid XML.
Well Formed XML Documents A "Well Formed" XML document has correct XML syntax. A "Well Formed" XML document is a document that conforms to the XML syntax rules that were described in the previous chapters: • • • • •
XML documents must have a root element XML elements must have a closing tag XML tags are case sensitive XML elements must be properly nested XML attribute values must always be quoted
<note> Tove Jani Reminder Don't forget me this weekend!
Valid XML Documents A "Valid" XML document also conforms to a DTD. A "Valid" XML document is a "Well Formed" XML document, which also conforms to the rules of a Document Type Definition (DTD):
<note> Tove Jani Reminder Don't forget me this weekend!
The purpose of a DTD is to define the legal building blocks of an XML document. It defines the document structure with a list of legal elements.
XML Validator
XML Browser Support Nearly all major browsers have support for XML and XSLT.
Mozilla Firefox As of version 1.0.2, Firefox has support for XML and XSLT (and CSS).
Mozilla Mozilla includes Expat for XML parsing and has support to display XML + CSS. Mozilla also has some support for Namespaces. Mozilla is available with an XSLT implementation.
Netscape As of version 8, Netscape uses the Mozilla engine, and therefore it has the same XML / XSLT support as Mozilla.
Opera As of version 9, Opera has support for XML and XSLT (and CSS). Version 8 supports only XML + CSS.
Internet Explorer As of version 6, Internet Explorer supports XML, Namespaces, CSS, XSLT, and XPath. Note: Internet Explorer 5 also has XML support, but the XSL part is NOT compatible with the official W3C XSL Recommendation!
Viewing XML Files Raw XML files can be viewed in Mozilla, Firefox, Opera, Internet Explorer, and Netscape 6+. However, to make XML documents display as nice web pages, you will have to add some display information.
Viewing XML Files In Firefox and Internet Explorer: Open the XML file (typically by clicking on a link) The XML document will be displayed with colorcoded root and child structure. To view the raw XML source (without the + and signs), select "View Page Source" or "View Source" from the elements. A plus (+) or minus sign () to the left of the elements can be clicked to expand or collapse the element browser menu. In Netscape 6: Open the XML file, then rightclick in XML file and select "View Page Source". The XML document will then be displayed with colorcoded root and child elements. In Opera 7 and 8:
document will be displayed as plain text. Note: Do not expect XML files to be formatted like HTML documents!
Viewing an Invalid XML File If an erroneous XML file is opened, the browser will report the error.
Why Does XML Display Like This? XML documents do not carry information about how to display the data. Since XML tags are "invented" by the author of the XML document, browsers do not know if a tag like describes an HTML table or a dining table. Without any information about how to display the data, most browsers will just display the XML document as it is. In the next chapters, we will take a look at different solutions to the display problem, using CSS, XSL, JavaScript, and XML Data Islands.
Displaying XML with CSS With CSS (Cascading Style Sheets) you can add display information to an XML document.
Displaying your XML Files with CSS? It is possible to use CSS to format an XML document. Below is a fraction of the XML file. The second line, , links the XML file to the CSS file:
<TITLE>Empire Burlesque Bob Dylan USA Columbia 10.90 1985 <TITLE>Hide your heart Bonnie Tyler UK CBS Records 9.90 1988 . . . .
Note: Formatting XML with CSS is NOT the future of how to style XML documents. XML document should be styled by using the W3C's XSL standard! The CSS file is shown below CATALOG { backgroundcolor: #ffffff; width: 100%; } CD { display: block; marginbottom: 30pt; marginleft: 0; } TITLE { color: #FF0000; fontsize: 20pt; } ARTIST { color: #0000FF; fontsize: 20pt; } COUNTRY,PRICE,YEAR,COMPANY { display: block;
color: #000000; marginleft: 20pt; }
Displaying XML with XSL With XSL you can add display information to your XML document.
Displaying XML with XSL XSL is the preferred style sheet language of XML. XSL (the eXtensible Stylesheet Language) is far more sophisticated than CSS. One way to use XSL is to transform XML into HTML before it is displayed by the browser as demonstrated in these examples: Below is a fraction of the XML file. The second line, , links the XML file to the XSL file: Belgian Waffles <price>$5.95 <description> two of our famous Belgian Waffles 650
XML Data Island With Internet Explorer, the unofficial <xml> tag can be used to create an XML data island.
XML Data Embedded in HTML An XML data island is XML data embedded into an HTML page. Here is how it works; assume we have the following XML document ("note.xml"):
<note> Tove Jani Reminder Don't forget me this weekend!
Then, in an HTML document, you can embed the XML file above with the <xml> tag. The id attribute of the <xml> tag defines an ID for the data island, and the src attribute points to the XML file to embed: <xml id="note" src="note.xml">
However, the embedded XML data is, up to this point, not visible for the user. The next step is to format and display the data in the data island by binding it to HTML elements.
Bind Data Island to HTML Elements
The HTML file looks like this: <xml id="cdcat" src="cd_catalog.xml"> <span datafld="ARTIST"> <span datafld="TITLE">
Example explained: The datasrc attribute of the tag binds the HTML table element to the XML data island. The datasrc attribute refers to the id attribute of the data island.
the <TITLE> element in the XML file. As the XML is read, additional rows are created for each element.
XML in Real Life A reallife example of how XML can be used to carry information.
Example: XML News XMLNews is a specification for exchanging news and other information. Using such a standard makes it easier for both news producers and news consumers to produce, receive, and archive any kind of news information across different hardware, software, and programming languages. An example XMLNews document: Colombia Earthquake 143 Dead in Colombia Earthquake By Jared Kotler, Associated Press Writer Bogota, Colombia Monday January 25 1999 7:28 ET
XML Parser
To read and update, create and manipulate an XML document, you will need an XML parser.
Parsing XML Documents To manipulate an XML document, you need an XML parser. The parser loads the document into your computer's memory. Once the document is loaded, its data can be manipulated using the DOM. The DOM treats the XML document as a tree. There are some differences between Microsoft's XML parser and the XML parser used in Mozilla browsers. In this tutorial we will show you how to create cross browser scripts that will work in both Internet Explorer and Mozilla browsers.
Microsoft's XML Parser Microsoft's XML parser is a COM component that comes with Internet Explorer 5 and higher. Once you have installed Internet Explorer, the parser is available to scripts.
To create an instance of Microsoft's XML parser, use the following code: JavaScript: var xmlDoc=new ActiveXObject("Microsoft.XMLDOM");
VBScript: set xmlDoc=CreateObject("Microsoft.XMLDOM")
ASP: set xmlDoc=Server.CreateObject("Microsoft.XMLDOM")
The following code fragment loads an existing XML document ("note.xml") into Microsoft's XML parser: var xmlDoc=new ActiveXObject("Microsoft.XMLDOM"); xmlDoc.async="false"; xmlDoc.load("note.xml");
The first line of the script above creates an instance of the XML parser. The second line turns off asynchronized loading, to make sure that the parser will not continue execution of the script before the document is fully loaded. The third line tells the parser to load an XML document called "note.xml".
XML Parser in Mozilla, Firefox, and Opera
To create an instance of the XML parser in Mozilla browsers, use the following code: JavaScript: var xmlDoc=document.implementation.createDocument("ns","root",null);
The first parameter, ns, defines the namespace used for the XML document. The second parameter, root, is the XML root element in the XML file. The third parameter, null, is always null because it is not implemented yet. The following code fragment loads an existing XML document ("note.xml") into Mozillas' XML parser: var xmlDoc=document.implementation.createDocument("","",null); xmlDoc.load("note.xml");
The first line of the script above creates an instance of the XML parser. The second line tells the parser to load an XML document called "note.xml".
Parsing an XML File A Cross browser Example The following example is a cross browser example that loads an existing XML document ("note.xml") into the XML parser:
<script type="text/javascript"> var xmlDoc; function loadXML() { // code for IE if (window.ActiveXObject) { xmlDoc=new ActiveXObject("Microsoft.XMLDOM"); xmlDoc.async=false; xmlDoc.load("note.xml"); getmessage(); } // code for Mozilla, Firefox, Opera, etc. else if (document.implementation && document.implementation.createDocument) { xmlDoc=document.implementation.createDocument("","",null); xmlDoc.load("note.xml"); xmlDoc.onload=getmessage; } else { alert('Your browser cannot handle this script'); } } function getmessage() { document.getElementById("to").innerHTML= xmlDoc.getElementsByTagName("to")[0].childNodes[0].nodeValue; document.getElementById("from").innerHTML= xmlDoc.getElementsByTagName("from")[0].childNodes[0].nodeValue; document.getElementById("message").innerHTML= xmlDoc.getElementsByTagName("body")[0].childNodes[0].nodeValue; } W3Schools Internal Note
To: <span id="to">
Output:
W3Schools Internal Note
To: Tove From: Jani Message: Don't forget me this weekend!
Important Note To extract the text (Jani) from an XML element like: Jani , the correct syntax is: getElementsByTagName("from")[0].childNodes[0].nodeValue
Parsing an XML String A Cross browser Example The following code is a crossbrowser example on how to load and parse an XML string: <script type="text/javascript"> var text="<note>"; text=text+"Tove "; text=text+"Jani "; text=text+"Reminder "; text=text+"Don't forget me this weekend!"; text=text+""; // code for IE if (window.ActiveXObject) { var doc=new ActiveXObject("Microsoft.XMLDOM"); doc.async="false"; doc.loadXML(text); } // code for Mozilla, Firefox, Opera, etc. else { var parser=new DOMParser(); var doc=parser.parseFromString(text,"text/xml"); } // documentElement always represents the root node var x=doc.documentElement; document.write("Text of first child element: "); document.write(x.childNodes[0].childNodes[0].nodeValue); document.write("
Output: Text of second child element: Jani Note: Internet Explorer uses the loadXML() method to parse an XML string, while Mozilla browsers uses the DOMParser object.
XML Namespaces XML Namespaces provide a method to avoid element name conflicts.
Name Conflicts Since element names in XML are not predefined, a name conflict will occur when two different documents use the same element names. This XML document carries information in a table: Apples Bananas
This XML document carries information about a table (a piece of furniture): African Coffee Table <width>80 120
If these two XML documents were added together, there would be an element name conflict because both documents contain a element with different content and definition.
Solving Name Conflicts Using a Prefix This XML document carries information in a table:
Apples Bananas
This XML document carries information about a piece of furniture: African Coffee Table 80 120
Now there will be no name conflict because the two documents use a different name for their element ( and ). By using a prefix, we have created two different types of elements.
Using Namespaces This XML document carries information in a table: Apples Bananas
This XML document carries information about a piece of furniture: African Coffee Table 80 120
Instead of using only prefixes, we have added an xmlns attribute to the tag to give the prefix a qualified name associated with a namespace.
The XML Namespace (xmlns) Attribute The XML namespace attribute is placed in the start tag of an element and has the following syntax: xmlns:namespaceprefix="namespaceURI"
When a namespace is defined in the start tag of an element, all child elements with the same prefix are associated with the same namespace. Note that the address used to identify the namespace is not used by the parser to look up information. The only purpose page containing information about the namespace. is to give the namespace a unique name. However, very often companies use the namespace as a pointer to a real Web Try to go to http://www.w3.org/TR/html4/.
Uniform Resource Identifier (URI) A Uniform Resource Identifier (URI) is a string of characters which identifies an Internet Resource. The most common URI is the Uniform Resource Locator (URL) which identifies an Internet domain address. Another, not so common type of URI is the Universal Resource Name (URN). In our examples we will only use URLs.
Default Namespaces Defining a default namespace for an element saves us from using prefixes in all the child elements. It has the following syntax: xmlns="namespaceURI"
This XML document carries information in a table: Apples Bananas
This XML document carries information about a piece of furniture: African Coffee Table <width>80 120
Namespaces in Real Use When you start using XSL, you will soon see namespaces in real use. XSL style sheets are used to transform XML documents into other formats, like HTML.
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> <xsl:template match="/"> My CD Collection
Title Artist <xsl:foreach select="catalog/cd"> <xsl:valueof select="title"/> <xsl:valueof select="artist"/>
XML CDATA All text in an XML document will be parsed by the parser. Only text inside a CDATA section will be ignored by the parser.
Parsed Data XML parsers normally parse all the text in an XML document. When an XML element is parsed, the text between the XML tags is also parsed: <message>This text is also parsed
The parser does this because XML elements can contain other elements, as in this example, where the element contains two other elements (first and last): Bill Gates
and the parser will break it up into subelements like this: Bill Gates
Escape Characters Illegal XML characters have to be replaced by entity references. If you place a character like "<" inside an XML element, it will generate an error because the parser interprets it as the start of a new element. You cannot write something like this: <message>if salary < 1000 then
To avoid this, you have to replace the "<" character with an entity reference, like this:
<message>if salary < 1000 then
There are 5 predefined entity references in XML: <
<
less than
>
>
greater than
&
&
ampersand
'
'
apostrophe
"
"
quotation mark
CDATA Everything inside a CDATA section is ignored by the parser. If your text contains a lot of "<" or "&" characters as program code often does the XML element can be defined as a CDATA section. A CDATA section starts with "": <script>
In the example above, everything inside the CDATA section is ignored by the parser.
Notes on CDATA sections: A CDATA section cannot contain the string "]]>", therefore, nested CDATA sections are not allowed.
XML Encoding XML documents may contain foreign characters, like Norwegian æ ø å , or French ê è é. To let your XML parser understand these characters, you should save your XML documents as Unicode.
Windows 2000 Notepad Windows 2000 Notepad can save files as Unicode. Save the XML file below as Unicode (note that the document does not contain any encoding attribute): <note> Jani Tove <message>Norwegian: æøå. French: êèé
The file above, will NOT generate an error in IE 5+, Firefox, or Opera, but it WILL generate an error in Netscape 6.2.
Windows 2000 Notepad with Encoding Windows 2000 Notepad files saved as Unicode use "UTF16" encoding. If you add an encoding attribute to XML files saved as Unicode, windows encoding values will generate an error. The following encoding will NOT give an error message:
The following encoding will NOT give an error message:
The following encoding will NOT give an error message:
The following encoding will NOT generate an error in IE 5+, Firefox, or Opera, but it WILL generate an error in Netscape 6.2.
Error Messages If you try to load an XML document into Internet Explorer, you can get two different errors indicating encoding problems: An invalid character was found in text content. You will get this error message if a character in the XML document does not match the encoding attribute. Normally you will get this error message if your XML document contains "foreign" characters, and the file was saved with a singlebyte encoding editor like Notepad, and no encoding attribute was specified. Switch from current encoding to specified encoding not supported. You will get this error message if your file was saved as Unicode/UTF16 but the encoding attribute specified a single byte encoding like Windows1252, ISO88591 or UTF8. You can also get this error message if your document was saved with singlebyte encoding, but the encoding attribute specified a doublebyte encoding like UTF16.
Conclusion The conclusion is that the encoding attribute has to specify the encoding used when the document was saved. My best advice to avoid errors is: • • •
Use an editor that supports encoding Make sure you know what encoding it uses Use the same encoding attribute in your XML documents
XML on the Server XML can be generated on a server without installing any XML controls.
Storing XML on the Server XML files can be stored on an Internet server exactly the same way as HTML files. Start Windows Notepad and write the following lines: <note> Jani Tove <message>Remember me this weekend
Save the file on your web server with a proper name like "note.xml".
Generating XML with ASP XML can be generated on a server without any installed XML software. To generate an XML response from the server simply write the following code and save it as an ASP file on the web server: <% response.ContentType="text/xml" response.Write("") response.Write("<note>") response.Write("Jani ") response.Write("Tove ") response.Write("<message>Remember me this weekend") response.Write("") %>
Note that the content type of the response must be set to "text/xml".
Getting XML From a Database XML can be generated from a database without any installed XML software. To generate an XML database response from the server, simply write the following code and save it as an ASP file on the web server: <% response.ContentType = "text/xml" conn.provider="Microsoft.Jet.OLEDB.4.0;" conn.open server.mappath("/db/database.mdb") sql="select fname,lname from tblGuestBook" set rs=Conn.Execute(sql) rs.MoveFirst() response.write("") response.write("") while (not rs.EOF) response.write("") response.write("" & rs("fname") & " ") response.write("" & rs("lname") & " ") response.write(" ") rs.MoveNext() wend rs.close() conn.close() response.write(" ") %>
The example above uses
XML Application This chapter demonstrates a small framework for an XML application. Note: This example uses a Data Island, which only works in Internet Explorer.
The XML Example Document Look at the following XML document ("cd_catalog.xml"), that represents a CD catalog: <TITLE>Empire Burlesque Bob Dylan USA Columbia 10.90 1985 . . ... more ... .
Load the XML Document into a Data Island A Data Island can be used to access the XML file. To get your XML document "inside" an HTML page, add an XML Data Island to the HTML page: <xml src="cd_catalog.xml" id="xmldso" async="false">
With the example code above, the XML file "cd_catalog.xml" will be loaded into an "invisible" Data Island called "xmldso". The async="false" attribute is added to make sure that all the XML data is loaded before any other HTML processing takes place.
Bind the Data Island to an HTML Table To make the XML data visible on the HTML page, you must "bind" the Data Island to an HTML element. To bind the XML data to an HTML table, add a datasrc attribute to the table element, and add datafld attributes to the span elements inside the table data: Title Artist Year <span datafld="TITLE"> <span datafld="ARTIST"> <span datafld="YEAR">
If you have IE 5.0 or higher
Bind the Data Island to <span> or Elements <span> or elements can be used to display XML data. You don't have to use the HTML table element to display XML data. Data from a Data Island can be displayed anywhere on an HTML page. All you have to do is to add some <span> or elements to your page. Use the datasrc attribute to bind the elements to the Data Island, and the datafld attribute to bind each element to an XML element, like this:
or like this:
Note that if you use an HTML element, the data will be displayed on a new line. With the examples above, you will only see one line of your XML data. To navigate to the next line of data, you have to add some scripting to your code.
Add a Navigation Script Navigation has to be performed by a script. To add navigation to the XML Data Island, create a script that calls the movenext() and moveprevious() methods of the Data Island. <script type="text/javascript"> function movenext() { x=xmldso.recordset if (x.absoluteposition < x.recordcount) { x.movenext() } } function moveprevious() { x=xmldso.recordset if (x.absoluteposition > 1) { x.moveprevious() } }
The XMLHttpRequest Object The XMLHttpRequest object is supported in Internet Explorer 5.0+, Safari 1.2, Mozilla 1.0 / Firefox, Opera 9, and Netscape 7.
What is an HTTP Request? With an HTTP request, a web page can make a request to, and get a response from a web server without reloading the page. The user will stay on the same page, and he or she will not notice that scripts might request pages, or send data to a server in the background. By using the XMLHttpRequest object, a web developer can change a page with data from the server after the page has loaded. Google Suggest is using the XMLHttpRequest object to create a very dynamic web interface: When you start typing in Google's search box, a JavaScript sends the letters off to a server and the server returns a list of suggestions.
Is the XMLHttpRequest Object a W3C Standard? The XMLHttpRequest object is a JavaScript object, and is not specified in any W3C recommendation. However, the W3C DOM Level 3 "Load and Save" specification contains some similar functionality, but these are not implemented in any browsers yet. So, at the moment, if you need to send an HTTP request from a browser, you will have to use the XMLHttpRequest object.
Creating an XMLHttpRequest Object For Mozilla, Firefox, Safari, Opera, and Netscape: var xmlhttp=new XMLHttpRequest()
For Internet Explorer: var xmlhttp=new ActiveXObject("Microsoft.XMLHTTP")
Example <script type="text/javascript"> var xmlhttp function loadXMLDoc(url) { xmlhttp=null // code for Mozilla, etc. if (window.XMLHttpRequest) { xmlhttp=new XMLHttpRequest() } // code for IE else if (window.ActiveXObject) { xmlhttp=new ActiveXObject("Microsoft.XMLHTTP") } if (xmlhttp!=null) { xmlhttp.onreadystatechange=state_Change xmlhttp.open("GET",url,true) xmlhttp.send(null) } else { alert("Your browser does not support XMLHTTP.") } } function state_Change() { // if xmlhttp shows "loaded" if (xmlhttp.readyState==4) { // if "OK" if (xmlhttp.status==200) { // ...some code here... } else { alert("Problem retrieving XML data") } } }
Note: An important property in the example above is the onreadystatechange property. This property is an event handler having the function xmlhttpChange() check for the state changing, we can tell when the process is complete and which is triggered each time the state of the request changes. The states run from 0 (uninitialized) to 4 (complete). By continue only if it has been successful.
Why are we Using Async in our Examples? All the examples here use the async mode (the third parameter of open() set to true). The async parameter specifies whether the request should be handled asynchronously or not. True means that script a user may even see the "Not Responding" message. It is safer to send asynchronously and design your code around script hang if there is a network or server problem, or if the request is long (the UI locks while the request is being made) for a response before continuing script processing. By setting this parameter to false, you run the risk of having your continues to run after the send() method, without waiting for a response from the server. false means that the script waits the onreadystatechange event!
The XMLHttpRequest Object Reference Methods Method
Description
abort()
Cancels the current request
getAllResponseHeaders()
Returns the complete set of http headers as a string
getResponseHeader("headername")
Returns the value of the specified http header
open("method","URL",async,"uname","pswd")
request sending data (especially if the length of the data is greater than "PUT" (use "GET" when requesting data and use "POST" when The method parameter can have a value of "GET", "POST", or 512 bytes. The URL parameter may be either a relative or complete URL. The async parameter specifies whether the request should be a response. false means that the script waits for a response processing carries on after the send() method, without waiting for handled asynchronously or not. true means that script before continuing script processing
send(content)
Sends the request
setRequestHeader("label","value")
Adds a label/value pair to the http header to be sent
Properties Property
Description
onreadystatechange
An event handler for an event that fires at every state change
readyState
Returns the state of the object:
responseText
Returns the response as a string
responseXML
properties
status
Returns the status as a number (e.g. 404 for "Not Found" or 200 for "OK")
statusText
Returns the status as a string (e.g. "Not Found" or "OK")
Save Data to an XML File Usually, we save data in databases. However, if we want to make the data more portable, we can store the data in an XML file.
Create and Save an XML File
Storing data in XML files is useful if the data is to be sent to applications on nonWindows platforms. Remember that XML is portable across all platforms and the data will not need to be converted! First we will learn how to create and save an XML file. The XML file below will be named "test.xml" and will be stored in the c directory on the server. We will use ASP and Microsoft's XMLDOM object to create and save the XML file: <% Dim xmlDoc, rootEl, child1, child2, p 'Create an XML document Set xmlDoc = Server.CreateObject("Microsoft.XMLDOM") 'Create a root element and append it to the document Set rootEl = xmlDoc.createElement("root") xmlDoc.appendChild rootEl 'Create and append child elements Set child1 = xmlDoc.createElement("child1") Set child2 = xmlDoc.createElement("child2") rootEl.appendChild child1 rootEl.appendChild child2 'Add an XML processing instruction 'and insert it before the root element Set p=xmlDoc.createProcessingInstruction("xml","version='1.0'") xmlDoc.insertBefore p,xmlDoc.childNodes(0) 'Save the XML file to the c directory xmlDoc.Save "c:\test.xml" %>
Real Form Example Now, we will look at a real HTML form example. We will first look at the HTML form that will be used in this example: The HTML form below asks for the user's name, country, and email address. This information will then be written to an XML file for storage. "customers.htm": Enter your contact information
First Name:
The action for the HTML form above is set to "saveForm.asp". The "saveForm.asp" file is an ASP page that will loop through the form fields and store their values in an XML file:
<% dim xmlDoc dim rootEl,fieldName,fieldValue,attID dim p,i 'Do not stop if an error occurs On Error Resume Next Set xmlDoc = server.CreateObject("Microsoft.XMLDOM") xmlDoc.preserveWhiteSpace=true 'Create a root element and append it to the document Set rootEl = xmlDoc.createElement("customer") xmlDoc.appendChild rootEl 'Loop through the form collection for i = 1 To Request.Form.Count 'Eliminate button elements in the form if instr(1,Request.Form.Key(i),"btn_")=0 then 'Create a field and a value element, and an id attribute Set fieldName = xmlDoc.createElement("field") Set fieldValue = xmlDoc.createElement("value") Set attID = xmlDoc.createAttribute("id") 'Set the value of the id attribute equal to the name of 'the current form field attID.Text = Request.Form.Key(i) 'Append the id attribute to the field element fieldName.setAttributeNode attID 'Set the value of the value element equal to 'the value of the current form field fieldValue.Text = Request.Form(i) 'Append the field element as a child of the root element rootEl.appendChild fieldName 'Append the value element as a child of the field element fieldName.appendChild fieldValue end if next 'Add an XML processing instruction 'and insert it before the root element Set p = xmlDoc.createProcessingInstruction("xml","version='1.0'") xmlDoc.insertBefore p,xmlDoc.childNodes(0) 'Save the XML file xmlDoc.save "c:\Customer.xml" 'Release all object references set xmlDoc=nothing set rootEl=nothing set fieldName=nothing set fieldValue=nothing set attID=nothing set p=nothing 'Test to see if an error occurred if err.number<>0 then response.write("Error: No information saved.") else response.write("Your information has been saved.") end if %>
Note: If the XML file name specified already exists, it will be overwritten! The XML file that will be produced by the code above will look something like this ("Customer.xml"): <customer>
XML DHTML Behaviors Internet Explorer 5 introduced DHTML behaviors. Behaviors are a way to add DHTML functionality to HTML elements with the ease of CSS.
Behaviors What are They? IE5 introduced DHTML behaviors. Behaviors are a way to add DHTML functionality to HTML elements with the ease of CSS. How do behaviors work? By using XML we can link behaviors to any element in a web page and manipulate that element. DHTML behaviors do not use a <script> tag. Instead, they are using a CSS attribute called "behavior". This "behavior" specifies a URL to an HTC file which contains the actual behavior (The HTC file is written in XML).
Syntax behavior: url(some_filename.htc)
Note: The behavior attribute is only supported by IE 5 and higher, all other browsers will ignore it. This means that Mozilla, Firefox, Netscape and other browsers will only see the regular content and IE 5+ can see the DHTML behaviors.
Example The following HTML file has a <style> element that defines a behavior for the element:
<style type="text/css"> h1 { behavior: url(behave.htc) } Mouse over me!!!
The XML document "behave.htc" is shown below: <script type="text/javascript"> function hig_lite() { element.style.color='red' } function low_lite() { element.style.color='blue' }
The behavior file contains a JavaScript and the event handlers for the script. The following HTML file has a <style> element that defines a behavior for elements with an id of "typing":
<style type="text/css"> #typing { behavior:url(typing.htc); fontfamily:'courier new'; } <span id="typing" speed="100">IE5 introduced DHTML behaviors. Behaviors are a way to add DHTML functionality to HTML elements with the ease of CSS.
The XML document "typing.htc" is shown below: <method name="type" /> <script type="text/javascript"> var i,text1,text2,textLength,t function beginTyping() { i=0 text1=element.innerText textLength=text1.length element.innerText="" text2="" t=window.setInterval(element.id+".type()",speed) } function type() { text2=text2+text1.substring(i,i+1) element.innerText=text2 i=i+1 if (i==textLength){clearInterval(t)} }
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XML is a Complement to HTML XML is not a replacement for HTML. It is important to understand that XML is not a replacement for HTML. In future Web development it is most likely that XML will be used to describe the data, while HTML will be used to format and display the same data. My best description of XML is this: XML is a crossplatform, software and hardware independent tool for transmitting information.
XML in Future Web Development XML is going to be everywhere. We have been participating in XML development since its creation. It has been amazing to see how quickly the XML standard has been developed and how quickly a large number of software vendors have adopted the standard. We strongly believe that XML will be as important to the future of the Web as HTML has been to the foundation of the Web and that XML will be the most common tool for all data manipulation and data transmission.
How can XML be Used? It is important to understand that XML was designed to store, carry, and exchange data. XML was not designed to display data.
XML can Separate Data from HTML With XML, your data is stored outside your HTML. When HTML is used to display data, the data is stored inside your HTML. With XML, data can be stored in separate XML files. This way you can concentrate on using HTML for data layout and display, and be sure that changes in the underlying data will not require any changes to your HTML. XML data can also be stored inside HTML pages as "Data Islands". You can still concentrate on using HTML only for formatting and displaying the data.
XML is Used to Exchange Data With XML, data can be exchanged between incompatible systems. In the real world, computer systems and databases contain data in incompatible formats. One of the most time consuming challenges for developers has been to exchange data between such systems over the Internet. Converting the data to XML can greatly reduce this complexity and create data that can be read by many different types of applications.
XML and B2B With XML, financial information can be exchanged over the Internet.
Expect to see a lot about XML and B2B (Business To Business) in the near future. XML is going to be the main language for exchanging financial information between businesses over the Internet. A lot of interesting B2B applications are under development.
XML Can be Used to Share Data With XML, plain text files can be used to share data. Since XML data is stored in plain text format, XML provides a software and hardwareindependent way of sharing data. This makes it much easier to create data that different applications can work with. It also makes it easier to expand or upgrade a system to new operating systems, servers, applications, and new browsers.
XML Can be Used to Store Data With XML, plain text files can be used to store data. XML can also be used to store data in files or in databases. Applications can be written to store and retrieve information from the store, and generic applications can be used to display the data.
XML Can Make your Data More Useful With XML, your data is available to more users. Since XML is independent of hardware, software and application, you can make your data available to other than only standard HTML browsers. Other clients and applications can access your XML files as data sources, like they are accessing databases. Your data can be made available to all kinds of "reading machines" (agents), and it is easier to make your data available for blind people, or people with other disabilities.
XML Can be Used to Create New Languages XML is the mother of WAP and WML.
If Developers Have Sense If they DO have sense, all future applications will exchange their data in XML. The future might give us word processors, spreadsheet applications and databases that can read each other's data in a pure text format, without any conversion utilities in between. We can only pray that Microsoft and all the other software vendors will agree.
XML Syntax Rules The syntax rules of XML are very simple and very strict. The rules are very easy to learn, and very easy to use. Because of this, creating software that can read and manipulate XML is very easy.
An Example XML Document XML documents use a selfdescribing and simple syntax. <note>
<note>
The next 4 lines describe 4 child elements of the root (to, from, heading, and body):
And finally the last line defines the end of the root element:
Can you detect from this example that the XML document contains a Note to Tove from Jani? Don't you agree that XML is pretty selfdescriptive?
All XML Elements Must Have a Closing Tag With XML, it is illegal to omit the closing tag. In HTML some elements do not have to have a closing tag. The following code is legal in HTML:
This is a paragraph
This is another paragraph
In XML all elements must have a closing tag, like this:
This is a paragraph
This is another paragraph
Note: You might have noticed from the previous example that the XML declaration did not have a closing tag. This is not an error. The declaration is not a part of the XML document itself. It is not an XML element, and it should not have a closing tag.
XML Tags are Case Sensitive Unlike HTML, XML tags are case sensitive. With XML, the tag
XML Elements Must be Properly Nested Improper nesting of tags makes no sense to XML.
In HTML some elements can be improperly nested within each other like this: This text is bold and italic
In XML all elements must be properly nested within each other like this: This text is bold and italic
XML Documents Must Have a Root Element All XML documents must contain a single tag pair to define a root element. All other elements must be within this root element. All elements can have sub elements (child elements). Sub elements must be correctly nested within their parent element:
XML Attribute Values Must be Quoted With XML, it is illegal to omit quotation marks around attribute values. XML elements can have attributes in name/value pairs just like in HTML. In XML the attribute value must always be quoted. Study the two XML documents below. The first one is incorrect, the second is correct: <note date=12/11/2002>
<note date="12/11/2002">
This is correct: date="12/11/2002". This is incorrect: date=12/11/2002.
With XML, White Space is Preserved With XML, the white space in your document is not truncated. This is unlike HTML. With HTML, a sentence like this: Hello my name is Tove, will be displayed like this: Hello my name is Tove, because HTML reduces multiple, consecutive white space characters to a single white space.
With XML, CR / LF is Converted to LF With XML, a new line is always stored as LF. Do you know what a typewriter is? Well, a typewriter is a mechanical device which was used last century to produce printed documents. :) After you have typed one line of text on a typewriter, you have to manually return the printing carriage to the left margin position and manually feed the paper up one line. In Windows applications, a new line is normally stored as a pair of characters: carriage return (CR) and line feed (LF). The character pair bears some resemblance to the typewriter actions of setting a new line. In Unix applications, a new line is normally stored as a LF character. Macintosh applications use only a CR character to store a new line.
Comments in XML The syntax for writing comments in XML is similar to that of HTML.
XML Elements XML Elements are extensible and they have relationships. XML Elements have simple naming rules.
XML Elements are Extensible XML documents can be extended to carry more information. Look at the following XML NOTE example: <note>
Let's imagine that we created an application that extracted the
<note>
Should the application break or crash? No. The application should still be able to find the
XML Elements have Relationships Elements are related as parents and children. To understand XML terminology, you have to know how relationships between XML elements are named, and how element content is described. Imagine that this is a description of a book: My First XML Introduction to XML • •
What is HTML What is XML
XML Syntax •
Elements must have a closing tag
•
Elements must be properly nested
Imagine that this XML document describes the book:
Book is the root element. Title, prod, and chapter are child elements of book. Book is the parent element of title, prod, and chapter. Title, prod, and chapter are siblings (or sister elements) because they have the same parent.
Elements have Content Elements can have different content types. An XML element is everything from (including) the element's start tag to (including) the element's end tag. An element can have element content, mixed content, simple content, or empty content. An element can also have attributes. In the example above, book has element content, because it contains other elements. Chapter has mixed content because it contains both text and other elements. Para has simple content (or text content) because it contains only text. Prod has empty content, because it carries no information. In the example above only the prod element has attributes. The attribute named id has the value "33657". The attribute named media has the value "paper".
Element Naming XML elements must follow these naming rules: • • • •
Names 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, etc) Names cannot contain spaces
Take care when you "invent" element names and follow these simple rules:
separator are nice. Examples:
XML Attributes XML elements can have attributes in the start tag, just like HTML. Attributes are used to provide additional information about elements.
XML Attributes XML elements can have attributes. From HTML you will remember this:
Attributes often provide information that is not a part of the data. In the example below, the file type is irrelevant to the data, but important to the software that wants to manipulate the element:
Quote Styles, "female" or 'female'?
Note: If the attribute value itself contains double quotes it is necessary to use single quotes, like in this example:
Note: If the attribute value itself contains single quotes it is necessary to use double quotes, like in this example:
Use of Elements vs. Attributes Data can be stored in child elements or in attributes. Take a look at these examples:
In the first example sex is an attribute. In the last, sex is a child element. Both examples provide the same information. There are no rules about when to use attributes, and when to use child elements. My experience is that attributes are handy in HTML, but in XML you should try to avoid them. Use child elements if the information feels like data.
My Favorite Way I like to store data in child elements.
<note date="12/11/2002">
A date element is used in the second example: <note>
An expanded date element is used in the third: (THIS IS MY FAVORITE): <note>
• • • • •
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 attribute values are not easy to test against a Document Type Definition (DTD) which is used to define the legal elements of an XML document
If you use attributes as containers for data, you end up with documents that are difficult to read and maintain. Try to use elements to describe data. Use attributes only to provide information that is not relevant to the data. Don't end up like this (this is not how XML should be used): <note day="12" month="11" year="2002" body="Don't forget me this weekend!">
An Exception to my Attribute Rule Rules always have exceptions. My rule about attributes has one exception: Sometimes I assign ID references to elements. These ID references can be used to access XML elements in much the same way as the NAME or ID attributes in HTML. This example demonstrates this: <messages> <note id="p501">
The ID in these examples is just a counter, or a unique identifier, to identify the different notes in the XML file, and not a part of the note data. What I am trying to say here is that metadata (data about data) should be stored as attributes, and that data itself should be stored as elements.
XML Validation XML with correct syntax is Well Formed XML. XML validated against a DTD is Valid XML.
Well Formed XML Documents A "Well Formed" XML document has correct XML syntax. A "Well Formed" XML document is a document that conforms to the XML syntax rules that were described in the previous chapters: • • • • •
XML documents must have a root element XML elements must have a closing tag XML tags are case sensitive XML elements must be properly nested XML attribute values must always be quoted
<note>
Valid XML Documents A "Valid" XML document also conforms to a DTD. A "Valid" XML document is a "Well Formed" XML document, which also conforms to the rules of a Document Type Definition (DTD):
<note>
The purpose of a DTD is to define the legal building blocks of an XML document. It defines the document structure with a list of legal elements.
XML Validator
XML Browser Support Nearly all major browsers have support for XML and XSLT.
Mozilla Firefox As of version 1.0.2, Firefox has support for XML and XSLT (and CSS).
Mozilla Mozilla includes Expat for XML parsing and has support to display XML + CSS. Mozilla also has some support for Namespaces. Mozilla is available with an XSLT implementation.
Netscape As of version 8, Netscape uses the Mozilla engine, and therefore it has the same XML / XSLT support as Mozilla.
Opera As of version 9, Opera has support for XML and XSLT (and CSS). Version 8 supports only XML + CSS.
Internet Explorer As of version 6, Internet Explorer supports XML, Namespaces, CSS, XSLT, and XPath. Note: Internet Explorer 5 also has XML support, but the XSL part is NOT compatible with the official W3C XSL Recommendation!
Viewing XML Files Raw XML files can be viewed in Mozilla, Firefox, Opera, Internet Explorer, and Netscape 6+. However, to make XML documents display as nice web pages, you will have to add some display information.
Viewing XML Files In Firefox and Internet Explorer: Open the XML file (typically by clicking on a link) The XML document will be displayed with colorcoded root and child structure. To view the raw XML source (without the + and signs), select "View Page Source" or "View Source" from the elements. A plus (+) or minus sign () to the left of the elements can be clicked to expand or collapse the element browser menu. In Netscape 6: Open the XML file, then rightclick in XML file and select "View Page Source". The XML document will then be displayed with colorcoded root and child elements. In Opera 7 and 8:
document will be displayed as plain text. Note: Do not expect XML files to be formatted like HTML documents!
Viewing an Invalid XML File If an erroneous XML file is opened, the browser will report the error.
Why Does XML Display Like This? XML documents do not carry information about how to display the data. Since XML tags are "invented" by the author of the XML document, browsers do not know if a tag like
| <span datafld="ARTIST"> | <span datafld="TITLE"> |
Example explained: The datasrc attribute of the
| Apples | Bananas |
This XML document carries information about a table (a piece of furniture):
If these two XML documents were added together, there would be an element name conflict because both documents contain a
| Apples | Bananas |
This XML document carries information about a piece of furniture:
Namespaces in Real Use When you start using XSL, you will soon see namespaces in real use. XSL style sheets are used to transform XML documents into other formats, like HTML.
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> <xsl:template match="/">
My CD Collection
XML CDATA All text in an XML document will be parsed by the parser. Only text inside a CDATA section will be ignored by the parser.
Parsed Data XML parsers normally parse all the text in an XML document. When an XML element is parsed, the text between the XML tags is also parsed: <message>This text is also parsed
The parser does this because XML elements can contain other elements, as in this example, where the
and the parser will break it up into subelements like this:
Escape Characters Illegal XML characters have to be replaced by entity references. If you place a character like "<" inside an XML element, it will generate an error because the parser interprets it as the start of a new element. You cannot write something like this: <message>if salary < 1000 then
To avoid this, you have to replace the "<" character with an entity reference, like this:
<message>if salary < 1000 then
There are 5 predefined entity references in XML: <
<
less than
>
>
greater than
&
&
ampersand
'
'
apostrophe
"
"
quotation mark
CDATA Everything inside a CDATA section is ignored by the parser. If your text contains a lot of "<" or "&" characters as program code often does the XML element can be defined as a CDATA section. A CDATA section starts with "": <script>
In the example above, everything inside the CDATA section is ignored by the parser.
Notes on CDATA sections: A CDATA section cannot contain the string "]]>", therefore, nested CDATA sections are not allowed.
XML Encoding XML documents may contain foreign characters, like Norwegian æ ø å , or French ê è é. To let your XML parser understand these characters, you should save your XML documents as Unicode.
Windows 2000 Notepad Windows 2000 Notepad can save files as Unicode. Save the XML file below as Unicode (note that the document does not contain any encoding attribute): <note>
The file above, will NOT generate an error in IE 5+, Firefox, or Opera, but it WILL generate an error in Netscape 6.2.
Windows 2000 Notepad with Encoding Windows 2000 Notepad files saved as Unicode use "UTF16" encoding. If you add an encoding attribute to XML files saved as Unicode, windows encoding values will generate an error. The following encoding will NOT give an error message:
The following encoding will NOT give an error message:
The following encoding will NOT give an error message:
The following encoding will NOT generate an error in IE 5+, Firefox, or Opera, but it WILL generate an error in Netscape 6.2.
Error Messages If you try to load an XML document into Internet Explorer, you can get two different errors indicating encoding problems: An invalid character was found in text content. You will get this error message if a character in the XML document does not match the encoding attribute. Normally you will get this error message if your XML document contains "foreign" characters, and the file was saved with a singlebyte encoding editor like Notepad, and no encoding attribute was specified. Switch from current encoding to specified encoding not supported. You will get this error message if your file was saved as Unicode/UTF16 but the encoding attribute specified a single byte encoding like Windows1252, ISO88591 or UTF8. You can also get this error message if your document was saved with singlebyte encoding, but the encoding attribute specified a doublebyte encoding like UTF16.
Conclusion The conclusion is that the encoding attribute has to specify the encoding used when the document was saved. My best advice to avoid errors is: • • •
Use an editor that supports encoding Make sure you know what encoding it uses Use the same encoding attribute in your XML documents
XML on the Server XML can be generated on a server without installing any XML controls.
Storing XML on the Server XML files can be stored on an Internet server exactly the same way as HTML files. Start Windows Notepad and write the following lines: <note>
Save the file on your web server with a proper name like "note.xml".
Generating XML with ASP XML can be generated on a server without any installed XML software. To generate an XML response from the server simply write the following code and save it as an ASP file on the web server: <% response.ContentType="text/xml" response.Write("") response.Write("<note>") response.Write("
Note that the content type of the response must be set to "text/xml".
Getting XML From a Database XML can be generated from a database without any installed XML software. To generate an XML database response from the server, simply write the following code and save it as an ASP file on the web server: <% response.ContentType = "text/xml" conn.provider="Microsoft.Jet.OLEDB.4.0;" conn.open server.mappath("/db/database.mdb") sql="select fname,lname from tblGuestBook" set rs=Conn.Execute(sql) rs.MoveFirst() response.write("") response.write("
The example above uses
XML Application This chapter demonstrates a small framework for an XML application. Note: This example uses a Data Island, which only works in Internet Explorer.
The XML Example Document Look at the following XML document ("cd_catalog.xml"), that represents a CD catalog:
Load the XML Document into a Data Island A Data Island can be used to access the XML file. To get your XML document "inside" an HTML page, add an XML Data Island to the HTML page: <xml src="cd_catalog.xml" id="xmldso" async="false">
With the example code above, the XML file "cd_catalog.xml" will be loaded into an "invisible" Data Island called "xmldso". The async="false" attribute is added to make sure that all the XML data is loaded before any other HTML processing takes place.
Bind the Data Island to an HTML Table To make the XML data visible on the HTML page, you must "bind" the Data Island to an HTML element. To bind the XML data to an HTML table, add a datasrc attribute to the table element, and add datafld attributes to the span elements inside the table data:
If you have IE 5.0 or higher
Bind the Data Island to <span> or
Elements <span> or
elements can be used to display XML data. You don't have to use the HTML table element to display XML data. Data from a Data Island can be displayed anywhere on an HTML page. All you have to do is to add some <span> or
elements to your page. Use the datasrc attribute to bind the elements to the Data Island, and the datafld attribute to bind each element to an XML element, like this:
or like this:
or like this:
Note that if you use an HTML
element, the data will be displayed on a new line. With the examples above, you will only see one line of your XML data. To navigate to the next line of data, you have to add some scripting to your code.
Add a Navigation Script Navigation has to be performed by a script. To add navigation to the XML Data Island, create a script that calls the movenext() and moveprevious() methods of the Data Island. <script type="text/javascript"> function movenext() { x=xmldso.recordset if (x.absoluteposition < x.recordcount) { x.movenext() } } function moveprevious() { x=xmldso.recordset if (x.absoluteposition > 1) { x.moveprevious() } }
The XMLHttpRequest Object The XMLHttpRequest object is supported in Internet Explorer 5.0+, Safari 1.2, Mozilla 1.0 / Firefox, Opera 9, and Netscape 7.
What is an HTTP Request? With an HTTP request, a web page can make a request to, and get a response from a web server without reloading the page. The user will stay on the same page, and he or she will not notice that scripts might request pages, or send data to a server in the background. By using the XMLHttpRequest object, a web developer can change a page with data from the server after the page has loaded. Google Suggest is using the XMLHttpRequest object to create a very dynamic web interface: When you start typing in Google's search box, a JavaScript sends the letters off to a server and the server returns a list of suggestions.
Is the XMLHttpRequest Object a W3C Standard? The XMLHttpRequest object is a JavaScript object, and is not specified in any W3C recommendation. However, the W3C DOM Level 3 "Load and Save" specification contains some similar functionality, but these are not implemented in any browsers yet. So, at the moment, if you need to send an HTTP request from a browser, you will have to use the XMLHttpRequest object.
Creating an XMLHttpRequest Object For Mozilla, Firefox, Safari, Opera, and Netscape: var xmlhttp=new XMLHttpRequest()
For Internet Explorer: var xmlhttp=new ActiveXObject("Microsoft.XMLHTTP")
Example <script type="text/javascript"> var xmlhttp function loadXMLDoc(url) { xmlhttp=null // code for Mozilla, etc. if (window.XMLHttpRequest) { xmlhttp=new XMLHttpRequest() } // code for IE else if (window.ActiveXObject) { xmlhttp=new ActiveXObject("Microsoft.XMLHTTP") } if (xmlhttp!=null) { xmlhttp.onreadystatechange=state_Change xmlhttp.open("GET",url,true) xmlhttp.send(null) } else { alert("Your browser does not support XMLHTTP.") } } function state_Change() { // if xmlhttp shows "loaded" if (xmlhttp.readyState==4) { // if "OK" if (xmlhttp.status==200) { // ...some code here... } else { alert("Problem retrieving XML data") } } }
Note: An important property in the example above is the onreadystatechange property. This property is an event handler having the function xmlhttpChange() check for the state changing, we can tell when the process is complete and which is triggered each time the state of the request changes. The states run from 0 (uninitialized) to 4 (complete). By continue only if it has been successful.
Why are we Using Async in our Examples? All the examples here use the async mode (the third parameter of open() set to true). The async parameter specifies whether the request should be handled asynchronously or not. True means that script a user may even see the "Not Responding" message. It is safer to send asynchronously and design your code around script hang if there is a network or server problem, or if the request is long (the UI locks while the request is being made) for a response before continuing script processing. By setting this parameter to false, you run the risk of having your continues to run after the send() method, without waiting for a response from the server. false means that the script waits the onreadystatechange event!
The XMLHttpRequest Object Reference Methods Method
Description
abort()
Cancels the current request
getAllResponseHeaders()
Returns the complete set of http headers as a string
getResponseHeader("headername")
Returns the value of the specified http header
open("method","URL",async,"uname","pswd")
request sending data (especially if the length of the data is greater than "PUT" (use "GET" when requesting data and use "POST" when The method parameter can have a value of "GET", "POST", or 512 bytes. The URL parameter may be either a relative or complete URL. The async parameter specifies whether the request should be a response. false means that the script waits for a response processing carries on after the send() method, without waiting for handled asynchronously or not. true means that script before continuing script processing
send(content)
Sends the request
setRequestHeader("label","value")
Adds a label/value pair to the http header to be sent
Properties Property
Description
onreadystatechange
An event handler for an event that fires at every state change
readyState
Returns the state of the object:
responseText
Returns the response as a string
responseXML
properties
status
Returns the status as a number (e.g. 404 for "Not Found" or 200 for "OK")
statusText
Returns the status as a string (e.g. "Not Found" or "OK")
Save Data to an XML File Usually, we save data in databases. However, if we want to make the data more portable, we can store the data in an XML file.
Create and Save an XML File
Storing data in XML files is useful if the data is to be sent to applications on nonWindows platforms. Remember that XML is portable across all platforms and the data will not need to be converted! First we will learn how to create and save an XML file. The XML file below will be named "test.xml" and will be stored in the c directory on the server. We will use ASP and Microsoft's XMLDOM object to create and save the XML file: <% Dim xmlDoc, rootEl, child1, child2, p 'Create an XML document Set xmlDoc = Server.CreateObject("Microsoft.XMLDOM") 'Create a root element and append it to the document Set rootEl = xmlDoc.createElement("root") xmlDoc.appendChild rootEl 'Create and append child elements Set child1 = xmlDoc.createElement("child1") Set child2 = xmlDoc.createElement("child2") rootEl.appendChild child1 rootEl.appendChild child2 'Add an XML processing instruction 'and insert it before the root element Set p=xmlDoc.createProcessingInstruction("xml","version='1.0'") xmlDoc.insertBefore p,xmlDoc.childNodes(0) 'Save the XML file to the c directory xmlDoc.Save "c:\test.xml" %>
Real Form Example Now, we will look at a real HTML form example. We will first look at the HTML form that will be used in this example: The HTML form below asks for the user's name, country, and email address. This information will then be written to an XML file for storage. "customers.htm":
The action for the HTML form above is set to "saveForm.asp". The "saveForm.asp" file is an ASP page that will loop through the form fields and store their values in an XML file:
<% dim xmlDoc dim rootEl,fieldName,fieldValue,attID dim p,i 'Do not stop if an error occurs On Error Resume Next Set xmlDoc = server.CreateObject("Microsoft.XMLDOM") xmlDoc.preserveWhiteSpace=true 'Create a root element and append it to the document Set rootEl = xmlDoc.createElement("customer") xmlDoc.appendChild rootEl 'Loop through the form collection for i = 1 To Request.Form.Count 'Eliminate button elements in the form if instr(1,Request.Form.Key(i),"btn_")=0 then 'Create a field and a value element, and an id attribute Set fieldName = xmlDoc.createElement("field") Set fieldValue = xmlDoc.createElement("value") Set attID = xmlDoc.createAttribute("id") 'Set the value of the id attribute equal to the name of 'the current form field attID.Text = Request.Form.Key(i) 'Append the id attribute to the field element fieldName.setAttributeNode attID 'Set the value of the value element equal to 'the value of the current form field fieldValue.Text = Request.Form(i) 'Append the field element as a child of the root element rootEl.appendChild fieldName 'Append the value element as a child of the field element fieldName.appendChild fieldValue end if next 'Add an XML processing instruction 'and insert it before the root element Set p = xmlDoc.createProcessingInstruction("xml","version='1.0'") xmlDoc.insertBefore p,xmlDoc.childNodes(0) 'Save the XML file xmlDoc.save "c:\Customer.xml" 'Release all object references set xmlDoc=nothing set rootEl=nothing set fieldName=nothing set fieldValue=nothing set attID=nothing set p=nothing 'Test to see if an error occurred if err.number<>0 then response.write("Error: No information saved.") else response.write("Your information has been saved.") end if %>
Note: If the XML file name specified already exists, it will be overwritten! The XML file that will be produced by the code above will look something like this ("Customer.xml"): <customer>
XML DHTML Behaviors Internet Explorer 5 introduced DHTML behaviors. Behaviors are a way to add DHTML functionality to HTML elements with the ease of CSS.
Behaviors What are They? IE5 introduced DHTML behaviors. Behaviors are a way to add DHTML functionality to HTML elements with the ease of CSS. How do behaviors work? By using XML we can link behaviors to any element in a web page and manipulate that element. DHTML behaviors do not use a <script> tag. Instead, they are using a CSS attribute called "behavior". This "behavior" specifies a URL to an HTC file which contains the actual behavior (The HTC file is written in XML).
Syntax behavior: url(some_filename.htc)
Note: The behavior attribute is only supported by IE 5 and higher, all other browsers will ignore it. This means that Mozilla, Firefox, Netscape and other browsers will only see the regular content and IE 5+ can see the DHTML behaviors.
Example The following HTML file has a <style> element that defines a behavior for the element:
Add a Navigation Script Navigation has to be performed by a script. To add navigation to the XML Data Island, create a script that calls the movenext() and moveprevious() methods of the Data Island. <script type="text/javascript"> function movenext() { x=xmldso.recordset if (x.absoluteposition < x.recordcount) { x.movenext() } } function moveprevious() { x=xmldso.recordset if (x.absoluteposition > 1) { x.moveprevious() } }
The XMLHttpRequest Object The XMLHttpRequest object is supported in Internet Explorer 5.0+, Safari 1.2, Mozilla 1.0 / Firefox, Opera 9, and Netscape 7.
What is an HTTP Request? With an HTTP request, a web page can make a request to, and get a response from a web server without reloading the page. The user will stay on the same page, and he or she will not notice that scripts might request pages, or send data to a server in the background. By using the XMLHttpRequest object, a web developer can change a page with data from the server after the page has loaded. Google Suggest is using the XMLHttpRequest object to create a very dynamic web interface: When you start typing in Google's search box, a JavaScript sends the letters off to a server and the server returns a list of suggestions.
Is the XMLHttpRequest Object a W3C Standard? The XMLHttpRequest object is a JavaScript object, and is not specified in any W3C recommendation. However, the W3C DOM Level 3 "Load and Save" specification contains some similar functionality, but these are not implemented in any browsers yet. So, at the moment, if you need to send an HTTP request from a browser, you will have to use the XMLHttpRequest object.
Creating an XMLHttpRequest Object For Mozilla, Firefox, Safari, Opera, and Netscape: var xmlhttp=new XMLHttpRequest()
For Internet Explorer: var xmlhttp=new ActiveXObject("Microsoft.XMLHTTP")
Example <script type="text/javascript"> var xmlhttp function loadXMLDoc(url) { xmlhttp=null // code for Mozilla, etc. if (window.XMLHttpRequest) { xmlhttp=new XMLHttpRequest() } // code for IE else if (window.ActiveXObject) { xmlhttp=new ActiveXObject("Microsoft.XMLHTTP") } if (xmlhttp!=null) { xmlhttp.onreadystatechange=state_Change xmlhttp.open("GET",url,true) xmlhttp.send(null) } else { alert("Your browser does not support XMLHTTP.") } } function state_Change() { // if xmlhttp shows "loaded" if (xmlhttp.readyState==4) { // if "OK" if (xmlhttp.status==200) { // ...some code here... } else { alert("Problem retrieving XML data") } } }
Note: An important property in the example above is the onreadystatechange property. This property is an event handler having the function xmlhttpChange() check for the state changing, we can tell when the process is complete and which is triggered each time the state of the request changes. The states run from 0 (uninitialized) to 4 (complete). By continue only if it has been successful.
Why are we Using Async in our Examples? All the examples here use the async mode (the third parameter of open() set to true). The async parameter specifies whether the request should be handled asynchronously or not. True means that script a user may even see the "Not Responding" message. It is safer to send asynchronously and design your code around script hang if there is a network or server problem, or if the request is long (the UI locks while the request is being made) for a response before continuing script processing. By setting this parameter to false, you run the risk of having your continues to run after the send() method, without waiting for a response from the server. false means that the script waits the onreadystatechange event!
The XMLHttpRequest Object Reference Methods Method
Description
abort()
Cancels the current request
getAllResponseHeaders()
Returns the complete set of http headers as a string
getResponseHeader("headername")
Returns the value of the specified http header
open("method","URL",async,"uname","pswd")
request sending data (especially if the length of the data is greater than "PUT" (use "GET" when requesting data and use "POST" when The method parameter can have a value of "GET", "POST", or 512 bytes. The URL parameter may be either a relative or complete URL. The async parameter specifies whether the request should be a response. false means that the script waits for a response processing carries on after the send() method, without waiting for handled asynchronously or not. true means that script before continuing script processing
send(content)
Sends the request
setRequestHeader("label","value")
Adds a label/value pair to the http header to be sent
Properties Property
Description
onreadystatechange
An event handler for an event that fires at every state change
readyState
Returns the state of the object:
responseText
Returns the response as a string
responseXML
properties
status
Returns the status as a number (e.g. 404 for "Not Found" or 200 for "OK")
statusText
Returns the status as a string (e.g. "Not Found" or "OK")
Save Data to an XML File Usually, we save data in databases. However, if we want to make the data more portable, we can store the data in an XML file.
Create and Save an XML File
Storing data in XML files is useful if the data is to be sent to applications on nonWindows platforms. Remember that XML is portable across all platforms and the data will not need to be converted! First we will learn how to create and save an XML file. The XML file below will be named "test.xml" and will be stored in the c directory on the server. We will use ASP and Microsoft's XMLDOM object to create and save the XML file: <% Dim xmlDoc, rootEl, child1, child2, p 'Create an XML document Set xmlDoc = Server.CreateObject("Microsoft.XMLDOM") 'Create a root element and append it to the document Set rootEl = xmlDoc.createElement("root") xmlDoc.appendChild rootEl 'Create and append child elements Set child1 = xmlDoc.createElement("child1") Set child2 = xmlDoc.createElement("child2") rootEl.appendChild child1 rootEl.appendChild child2 'Add an XML processing instruction 'and insert it before the root element Set p=xmlDoc.createProcessingInstruction("xml","version='1.0'") xmlDoc.insertBefore p,xmlDoc.childNodes(0) 'Save the XML file to the c directory xmlDoc.Save "c:\test.xml" %>
Real Form Example Now, we will look at a real HTML form example. We will first look at the HTML form that will be used in this example: The HTML form below asks for the user's name, country, and email address. This information will then be written to an XML file for storage. "customers.htm":
Enter your contact information
First Name:The action for the HTML form above is set to "saveForm.asp". The "saveForm.asp" file is an ASP page that will loop through the form fields and store their values in an XML file:
<% dim xmlDoc dim rootEl,fieldName,fieldValue,attID dim p,i 'Do not stop if an error occurs On Error Resume Next Set xmlDoc = server.CreateObject("Microsoft.XMLDOM") xmlDoc.preserveWhiteSpace=true 'Create a root element and append it to the document Set rootEl = xmlDoc.createElement("customer") xmlDoc.appendChild rootEl 'Loop through the form collection for i = 1 To Request.Form.Count 'Eliminate button elements in the form if instr(1,Request.Form.Key(i),"btn_")=0 then 'Create a field and a value element, and an id attribute Set fieldName = xmlDoc.createElement("field") Set fieldValue = xmlDoc.createElement("value") Set attID = xmlDoc.createAttribute("id") 'Set the value of the id attribute equal to the name of 'the current form field attID.Text = Request.Form.Key(i) 'Append the id attribute to the field element fieldName.setAttributeNode attID 'Set the value of the value element equal to 'the value of the current form field fieldValue.Text = Request.Form(i) 'Append the field element as a child of the root element rootEl.appendChild fieldName 'Append the value element as a child of the field element fieldName.appendChild fieldValue end if next 'Add an XML processing instruction 'and insert it before the root element Set p = xmlDoc.createProcessingInstruction("xml","version='1.0'") xmlDoc.insertBefore p,xmlDoc.childNodes(0) 'Save the XML file xmlDoc.save "c:\Customer.xml" 'Release all object references set xmlDoc=nothing set rootEl=nothing set fieldName=nothing set fieldValue=nothing set attID=nothing set p=nothing 'Test to see if an error occurred if err.number<>0 then response.write("Error: No information saved.") else response.write("Your information has been saved.") end if %>
Note: If the XML file name specified already exists, it will be overwritten! The XML file that will be produced by the code above will look something like this ("Customer.xml"): <customer>
XML DHTML Behaviors Internet Explorer 5 introduced DHTML behaviors. Behaviors are a way to add DHTML functionality to HTML elements with the ease of CSS.
Behaviors What are They? IE5 introduced DHTML behaviors. Behaviors are a way to add DHTML functionality to HTML elements with the ease of CSS. How do behaviors work? By using XML we can link behaviors to any element in a web page and manipulate that element. DHTML behaviors do not use a <script> tag. Instead, they are using a CSS attribute called "behavior". This "behavior" specifies a URL to an HTC file which contains the actual behavior (The HTC file is written in XML).
Syntax behavior: url(some_filename.htc)
Note: The behavior attribute is only supported by IE 5 and higher, all other browsers will ignore it. This means that Mozilla, Firefox, Netscape and other browsers will only see the regular content and IE 5+ can see the DHTML behaviors.
Example The following HTML file has a <style> element that defines a behavior for the
element:
<style type="text/css"> h1 { behavior: url(behave.htc) } Mouse over me!!!
The XML document "behave.htc" is shown below: <script type="text/javascript"> function hig_lite() { element.style.color='red' } function low_lite() { element.style.color='blue' }
The behavior file contains a JavaScript and the event handlers for the script. The following HTML file has a <style> element that defines a behavior for elements with an id of "typing":
<style type="text/css"> #typing { behavior:url(typing.htc); fontfamily:'courier new'; } <span id="typing" speed="100">IE5 introduced DHTML behaviors. Behaviors are a way to add DHTML functionality to HTML elements with the ease of CSS.
The XML document "typing.htc" is shown below: <method name="type" /> <script type="text/javascript"> var i,text1,text2,textLength,t function beginTyping() { i=0 text1=element.innerText textLength=text1.length element.innerText="" text2="" t=window.setInterval(element.id+".type()",speed) } function type() { text2=text2+text1.substring(i,i+1) element.innerText=text2 i=i+1 if (i==textLength){clearInterval(t)} }
The behavior file contains a JavaScript and the event handlers for the script. The following HTML file has a <style> element that defines a behavior for elements with an id of "typing":
<style type="text/css"> #typing { behavior:url(typing.htc); fontfamily:'courier new'; } <span id="typing" speed="100">IE5 introduced DHTML behaviors. Behaviors are a way to add DHTML functionality to HTML elements with the ease of CSS.
The XML document "typing.htc" is shown below:
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