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Learning XML language
XML Tutorial
Try-It-Yourself!
Start the XML Quiz!
What is XML, and how does it differ from HTML?
How XML can be used
Some of the different ways XML can be used.
XML Syntax
The strict and very simple syntax rules of XML.
XML Elements
XML Elements, relationships, content and naming rules.
XML Attributes
How XML attributes can be used to describe elements or provide additional information about elements.
XML Validation
The difference between a well-formed and a valid XML document, and how a DTD is used to define the structure of an XML document.
XML Validator
A simple on-line tool for syntax-checking XML.
XML Browser support
About the XML-support in the most common browsers.
Viewing XML in Browsers
How to view XML files.
Displaying XML with CSS
How to use CSS to display an XML file.
Displaying XML with XSL
How to use XSL to display an XML file.
XML embedded in HTML
How to embed XML inside HTML documents.
XML in Real Life
A real-life example of how XML can be used to carry information.
XML Parser
To read and update, create and manipulate an XML document, you will need an XML parser.
How to avoid element name conflicts using XML namespaces.
XML CDATA
How to tell an XML parser not to parse the text.
XML Encoding
How to encode your XML documents.
XML Server
How to generate XML on the server.
XML Applications
How to use IE to navigate in an XML file and how to create a complete XML application.
XML HTTP Requests
By using the XMLHttpRequest object, a web developer can change a page with data from the server after the page has loaded.
XML 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.
Behaviors for HTML and XML
How the CSS behavior selector can be used to create dynamic content.
XML Technologies
XML-related technologies.
XML Editor
Why you should use an XML editor when you edit XML documents.
XML Summary
This chapter contains a summary on what you have learned in this tutorial and a recommendation on what subject you should study next.
Lots of XML Examples !!
XML Quiz!
Test your XML skills at W3Schools!Introduction to XML
You can read more about XML standards in our W3C tutorial.
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.
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:
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.
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 <p>, <h1>, etc.).
XML allows the author to define his own tags and his own document structure.
The tags in the example above (like <to> and <from>) are not defined in any XML standard. These tags are "invented" by the author of the XML document.
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 cross-platform, software and hardware independent tool for transmitting information.
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.
Answer: When you need a buzzword in your resume.How can XML be Used?
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.
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.
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.
Since XML data is stored in plain text format, XML provides a software- and hardware-independent 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 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.
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.
The Wireless Markup Language (WML), used to markup Internet applications for handheld devices like mobile phones, is written in XML.
You can read more about WML in our WML tutorial.
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 first line in the document - the XML declaration - defines the XML version and the character encoding used in the document. In this case the document conforms to the 1.0 specification of XML and uses the ISO-8859-1 (Latin-1/West European) character set.
The next line describes the root element of the document (like it was saying: "this document is a note"):
The next 4 lines describe 4 child elements of the root (to, from, heading, and body):
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 self-descriptive?
In HTML some elements do not have to have a closing tag. The following code is legal in HTML:
In XML all elements must have a closing tag, like this:
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.
With XML, the tag <Letter> is different from the tag <letter>.
Opening and closing tags must therefore be written with the same case:
In HTML some elements can be improperly nested within each other like this:
In XML all elements must be properly nested within each other like this:
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 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:
The error in the first document is that the date attribute in the note element is not quoted.
This is correct: date="12/11/2002". This is incorrect: date=12/11/2002.
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.
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.
<!-- This is a comment -->
Software that can handle plain text can also handle XML. In a simple text editor, the XML tags will be visible and will not be handled specially.
In an XML-aware application however, the XML tags can be handled specially. The tags may or may not be visible, or have a functional meaning, depending on the nature of the application. XML Elements
Look at the following XML NOTE example:
Let's imagine that we created an application that extracted the <to>, <from>, and <body> elements from the XML document to produce this output:
Imagine that the author of the XML document added some extra information to it:
Should the application break or crash?
No. The application should still be able to find the <to>, <from>, and <body> elements in the XML document and produce the same output.
XML documents are Extensible.
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:
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.
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 "33-657". The attribute named media has the value "paper".
Any name can be used, no words are reserved, but the idea is to make names descriptive. Names with an underscore separator are nice.
Examples: <first_name>, <last_name>.
Avoid "-" and "." in names. For example, if you name something "first-name," 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: <book_title> not like this: <the_title_of_the_book>.
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.
Non-English 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
From HTML you will remember this: <IMG SRC="computer.gif">. 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:
or like this:
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:
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.
The following three XML documents contain exactly the same information:
A date attribute is used in the first example:
A date element is used in the second example:
An expanded date element is used in the third: (THIS IS MY FAVORITE):
Some of the problems with using attributes are:
Don't end up like this (this is not how XML should be used):
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:
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 with correct syntax is Well Formed XML. XML validated against a DTD is Valid XML.
A "Well Formed" XML document is a document that conforms to the XML syntax rules that were described in the previous chapters:
A "Valid" XML document is a "Well Formed" XML document, which also conforms to the rules of a Document Type Definition (DTD):
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. You can read more about DTD, and how to validate your XML documents in our DTD tutorial.
W3C supports an alternative to DTD called XML Schema. You can read more about XML Schema in our Schema tutorial.
The W3C XML specification states that a program should not continue to process an XML document if it finds an error. The reason is that XML software should be easy to write, and that all XML documents should be compatible.
With HTML it was possible to create documents with lots of errors (like when you forget an end tag). One of the main reasons that HTML browsers are so big and incompatible, is that they have their own ways to figure out what a document should look like when they encounter an HTML error.
With XML this should not be possible.
Paste your XML in the text area below, and syntax-check it by pressing the "Validate" button.
<?xml version="1.0" ?> <note> <to>Tove</to> <from>Jani</Ffrom> <heading>Reminder</heading> <body>Don't forget me this weekend!</body> </note>
Filename:
If you want to syntax-check an error-free XML file, you can paste the following address into the filename field: http://www.w3schools.com/xml/cd_catalog.xml
Note: If you get the error "Access denied" when accessing this file, it is because your Internet Explorer security settings do not allow access across domains! Nearly all major browsers have support for XML and XSLT.
Mozilla is available with an XSLT implementation.
Note: Internet Explorer 5 also has XML support, but the XSL part is NOT compatible with the official W3C XSL Recommendation!Viewing XML Files
Open the XML file (typically by clicking on a link) - The XML document will be displayed with color-coded root and child elements. A plus (+) or minus sign (-) to the left of the elements can be clicked to expand or collapse the element structure. To view the raw XML source (without the + and - signs), select "View Page Source" or "View Source" from the browser menu.
In Netscape 6:
Open the XML file, then right-click in XML file and select "View Page Source". The XML document will then be displayed with color-coded root and child elements.
In Opera 7 and 8:
In Opera 7: Open the XML file, then right-click in XML file and select "Frame" / "View Source". The XML document will be displayed as plain text. In Opera 8: Open the XML file, then right-click in XML file and select "Source". The XML document will be displayed as plain text.
Look at this XML file: note.xml
Note: Do not expect XML files to be formatted like HTML documents!
Look at this XML file: note_error.xml
An XML CD catalog
This is my father's CD collection, stored as XML data (old and boring titles I guess... :-)).
An XML plant catalog
This is a plant catalog from a plant shop, stored as XML data.
A Simple Food Menu
This is a breakfast food menu from a restaurant, stored as XML data.
Since XML tags are "invented" by the author of the XML document, browsers do not know if a tag like <table> 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
Below is an example of how to use a CSS style sheet to format an XML document:
Take a look at this XML file: The CD catalog
Then look at this style sheet: The CSS file
Finally, view: The CD catalog formatted with the CSS file
Below is a fraction of the XML file. The second line, <?xml-stylesheet type="text/css" href="cd_catalog.css"?>, links the XML file to the CSS file:
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!XML Data Island
Here is how it works; assume we have the following XML document ("note.xml"):
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:
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.
View "cd_catalog.xml".
The HTML file looks like this:
Example explained:
The datasrc attribute of the <table> tag binds the HTML table element to the XML data island. The datasrc attribute refers to the id attribute of the data island.
<td> tags cannot be bound to data, so we are using <span> tags. The <span> tag allows the datafld attribute to refer to the XML element to be displayed. In this case, it is datafld="ARTIST" for the <ARTIST> element and datafld="TITLE" for the <TITLE> element in the XML file. As the XML is read, additional rows are created for each <CD> element.
If you are running IE 5.0 or higher, you can try it yourself.
Also try this example, demonstrating <thead>, <tbody>, and <tfoot>.XML in Real Life
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:
XML Parser
This example is a cross-browser example that loads an existing XML document ("note.xml") into the XML parser.
Parse an XML string - Crossbrowser example
This example is a cross-browser example on how to load and parse an XML string.
To learn more about the XML DOM, please read our XML DOM tutorial.
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 supports all the necessary functions to traverse the node tree, access the nodes and their attribute values, insert and delete nodes, and convert the node tree back to XML.
To create an instance of Microsoft's XML parser, use the following code:
JavaScript:
VBScript:
ASP:
The following code fragment loads an existing XML document ("note.xml") into Microsoft's XML parser:
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".
To create an instance of the XML parser in Mozilla browsers, use the following code:
JavaScript:
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:
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".
Output:
IMPORTANT: getElementsByTagName returns an array of nodes. The array contains all elements with the specified name within the XML document. In this case there is only one "from" element, but you still have to specify the array index ( [0] ).
Output:
Note: Internet Explorer uses the loadXML() method to parse an XML string, while Mozilla browsers uses the DOMParser object.XML Namespaces
This XML document carries information in a table:
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 <table> element with different content and definition.
This XML document carries information about a piece of furniture:
Now there will be no name conflict because the two documents use a different name for their <table> element (<h:table> and <f:table>).
By using a prefix, we have created two different types of <table> elements.
This XML document carries information about a piece of furniture:
Instead of using only prefixes, we have added an xmlns attribute to the <table> tag to give the prefix a qualified name associated with a namespace.
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 is to give the namespace a unique name. However, very often companies use the namespace as a pointer to a real Web page containing information about the namespace.
Try to go to http://www.w3.org/TR/html4/.
This XML document carries information in a table:
This XML document carries information about a piece of furniture:
If you take a close look at the XSL document below, you will see that most of the tags are HTML tags. The tags that are not HTML tags have the prefix xsl, identified by the namespace "http://www.w3.org/1999/XSL/Transform":
XML CDATA
When an XML element is parsed, the text between the XML tags is also parsed:
The parser does this because XML elements can contain other elements, as in this example, where the <name> element contains two other elements (first and last):
and the parser will break it up into sub-elements like this:
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:
To avoid this, you have to replace the "<" character with an entity reference, like this:
There are 5 predefined entity references in XML:
Note: Only the characters "<" and "&" are strictly illegal in XML. Apostrophes, quotation marks and greater than signs are legal, but it is a good habit to replace them.
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 "<![CDATA[" and ends with "]]>":
In the example above, everything inside the CDATA section is ignored by the parser.
Also make sure there are no spaces or line breaks inside the "]]>" string. XML Encoding
Save the XML file below as Unicode (note that the document does not contain any encoding attribute):
The file above, note_encode_none_u.xml will NOT generate an error in IE 5+, Firefox, or Opera, but it WILL generate an error in Netscape 6.2.
If you add an encoding attribute to XML files saved as Unicode, windows encoding values will generate an error.
The following encoding (open it), will NOT give an error message:
The following encoding (open it), will NOT give an error message:
The following encoding (open it), will NOT give an error message:
The following encoding (open it), will NOT generate an error in IE 5+, Firefox, or Opera, but it WILL generate an error in Netscape 6.2.
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 single-byte 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/UTF-16 but the encoding attribute specified a single-byte encoding like Windows-1252, ISO-8859-1 or UTF-8. You can also get this error message if your document was saved with single-byte encoding, but the encoding attribute specified a double-byte encoding like UTF-16.
Start Windows Notepad and write the following lines:
Save the file on your web server with a proper name like "note.xml".
To generate an XML response from the server - simply write the following code and save it as an ASP file on the web server:
Note that the content type of the response must be set to "text/xml".
See how the ASP file will be returned from the server.
If you don't know how to write ASP, please visit our ASP tutorial
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:
See the real life database output from the ASP file above.
The example above uses ASP with ADO. If you don't know how to use ADO, please visit our ADO tutorial.XML Application
View the full "cd_catalog.xml" file in your browser.
To get your XML document "inside" an HTML page, add an XML Data Island to the HTML page:
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.
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: See how the XML data is displayed inside an HTML table.
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 <div> 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:
XML Tutorial
| | XML stands for EXtensible Markup Language. XML is designed to describe data and to focus on what data is. In our XML tutorial you will learn about XML and the difference between XML and HTML. You will also learn how to start using XML in your applications. Start learning XML! |
XML Examples
Learn by examples! With our editor, you can edit XML and click on a test button to view the result.Try-It-Yourself!
XML Quiz Test
Test your XML skills at W3Schools!Start the XML Quiz!
Table of Contents
XML Basic
Introduction to XMLWhat is XML, and how does it differ from HTML?
How XML can be used
Some of the different ways XML can be used.
XML Syntax
The strict and very simple syntax rules of XML.
XML Elements
XML Elements, relationships, content and naming rules.
XML Attributes
How XML attributes can be used to describe elements or provide additional information about elements.
XML Validation
The difference between a well-formed and a valid XML document, and how a DTD is used to define the structure of an XML document.
XML Validator
A simple on-line tool for syntax-checking XML.
XML Browser support
About the XML-support in the most common browsers.
Viewing XML in Browsers
How to view XML files.
Displaying XML with CSS
How to use CSS to display an XML file.
Displaying XML with XSL
How to use XSL to display an XML file.
XML embedded in HTML
How to embed XML inside HTML documents.
XML in Real Life
A real-life example of how XML can be used to carry information.
XML Parser
To read and update, create and manipulate an XML document, you will need an XML parser.
XML Advanced
XML NamespacesHow to avoid element name conflicts using XML namespaces.
XML CDATA
How to tell an XML parser not to parse the text.
XML Encoding
How to encode your XML documents.
XML Server
How to generate XML on the server.
XML Applications
How to use IE to navigate in an XML file and how to create a complete XML application.
XML HTTP Requests
By using the XMLHttpRequest object, a web developer can change a page with data from the server after the page has loaded.
XML 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.
Behaviors for HTML and XML
How the CSS behavior selector can be used to create dynamic content.
XML Technologies
XML-related technologies.
XML Editor
Why you should use an XML editor when you edit XML documents.
XML Summary
This chapter contains a summary on what you have learned in this tutorial and a recommendation on what subject you should study next.
XML Examples/Quiz
XML ExamplesLots of XML Examples !!
XML Quiz!
Test your XML skills at W3Schools!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 self-descriptive
- XML is a W3C Recommendation
XML is a W3C Recommendation
The Extensible Markup Language (XML) became a W3C Recommendation 10. February 1998.You can read more about XML standards in our W3C tutorial.
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><to>Tove</to><from>Jani</from><heading>Reminder</heading><body>Don't forget me this weekend!</body></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 <p>, <h1>, etc.).
XML allows the author to define his own tags and his own document structure.
The tags in the example above (like <to> and <from>) 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 cross-platform, 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.
XML Joke
Question: When should I use XML?Answer: When you need a buzzword in your resume.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 hardware-independent 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.The Wireless Markup Language (WML), used to markup Internet applications for handheld devices like mobile phones, is written in XML.
You can read more about WML in our WML tutorial.
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 self-describing and simple syntax.| <?xml version="1.0" encoding="ISO-8859-1"?><note><to>Tove</to><from>Jani</from><heading>Reminder</heading><body>Don't forget me this weekend!</body></note> |
The first line in the document - the XML declaration - defines the XML version and the character encoding used in the document. In this case the document conforms to the 1.0 specification of XML and uses the ISO-8859-1 (Latin-1/West European) character set.
The next line describes the root element of the document (like it was saying: "this document is a note"):
| <note> |
The next 4 lines describe 4 child elements of the root (to, from, heading, and body):
| <to>Tove</to><from>Jani</from><heading>Reminder</heading><body>Don't forget me this weekend!</body> |
And finally the last line defines the end of the root element:
| </note> |
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 self-descriptive?
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:
| <p>This is a paragraph<p>This is another paragraph |
In XML all elements must have a closing tag, like this:
| <p>This is a paragraph</p><p>This is another paragraph</p> |
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 <Letter> is different from the tag <letter>.
Opening and closing tags must therefore be written with the same case:
| <Message>This is incorrect</message> <message>This is correct</message> |
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:
| <b><i>This text is bold and italic</b></i> |
In XML all elements must be properly nested within each other like this:
| <b><i>This text is bold and italic</i></b> |
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:
| <root> <child> <subchild>.....</subchild> </child></root> |
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:
| <?xml version="1.0" encoding="ISO-8859-1"?><note date=12/11/2002><to>Tove</to><from>Jani</from></note> |
| <?xml version="1.0" encoding="ISO-8859-1"?><note date="12/11/2002"><to>Tove</to><from>Jani</from></note> |
The error in the first document is that the date attribute in the note element is not quoted.
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.<!-- This is a comment -->
There is Nothing Special About XML
There is nothing special about XML. It is just plain text with the addition of some XML tags enclosed in angle brackets.Software that can handle plain text can also handle XML. In a simple text editor, the XML tags will be visible and will not be handled specially.
In an XML-aware application however, the XML tags can be handled specially. The tags may or may not be visible, or have a functional meaning, depending on the nature of the application. 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><to>Tove</to><from>Jani</from><body>Don't forget me this weekend!</body></note> |
Let's imagine that we created an application that extracted the <to>, <from>, and <body> elements from the XML document to produce this output:
| MESSAGE 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><date>2002-08-01</date><to>Tove</to><from>Jani</from><heading>Reminder</heading><body>Don't forget me this weekend!</body></note> |
Should the application break or crash?
No. The application should still be able to find the <to>, <from>, and <body> 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
|
Imagine that this XML document describes the book:
| <book><title>My First XML</title><prod id="33-657" media="paper"></prod><chapter>Introduction to XML<para>What is HTML</para><para>What is XML</para></chapter> <chapter>XML Syntax<para>Elements must have a closing tag</para><para>Elements must be properly nested</para></chapter> </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 "33-657". 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
Any name can be used, no words are reserved, but the idea is to make names descriptive. Names with an underscore separator are nice.
Examples: <first_name>, <last_name>.
Avoid "-" and "." in names. For example, if you name something "first-name," 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: <book_title> not like this: <the_title_of_the_book>.
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.
Non-English 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: <IMG SRC="computer.gif">. The SRC attribute provides additional information about the IMG element.
In HTML (and in XML) attributes provide additional information about elements:
| <img src="computer.gif"><a href="demo.asp"> |
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:
| <file type="gif">computer.gif</file> |
Quote Styles, "female" or 'female'?
Attribute values must always be enclosed in quotes, but either single or double quotes can be used. For a person's sex, the person tag can be written like this:| <person sex="female"> |
or like this:
| <person sex='female'> |
Note: If the attribute value itself contains double quotes it is necessary to use single quotes, like in this example:
| <gangster name='George "Shotgun" Ziegler'> |
Note: If the attribute value itself contains single quotes it is necessary to use double quotes, like in this example:
| <gangster name="George 'Shotgun' Ziegler"> |
Use of Elements vs. Attributes
Data can be stored in child elements or in attributes.Take a look at these examples:
| <person sex="female"> <firstname>Anna</firstname> <lastname>Smith</lastname></person> |
| <person> <sex>female</sex> <firstname>Anna</firstname> <lastname>Smith</lastname></person> |
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.The following three XML documents contain exactly the same information:
A date attribute is used in the first example:
| <note date="12/11/2002"><to>Tove</to><from>Jani</from><heading>Reminder</heading><body>Don't forget me this weekend!</body></note> |
A date element is used in the second example:
| <note><date>12/11/2002</date><to>Tove</to><from>Jani</from><heading>Reminder</heading><body>Don't forget me this weekend!</body></note> |
An expanded date element is used in the third: (THIS IS MY FAVORITE):
| <note><date> <day>12</day> <month>11</month> <year>2002</year></date><to>Tove</to><from>Jani</from><heading>Reminder</heading><body>Don't forget me this weekend!</body></note> |
Avoid using attributes?
Should you avoid using attributes?Some of the problems with using attributes are:
- 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
Don't end up like this (this is not how XML should be used):
| <note day="12" month="11" year="2002"to="Tove" from="Jani" heading="Reminder" body="Don't forget me this weekend!"></note> |
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"> <to>Tove</to> <from>Jani</from> <heading>Reminder</heading> <body>Don't forget me this weekend!</body> </note> <note id="p502"> <to>Jani</to> <from>Tove</from> <heading>Re: Reminder</heading> <body>I will not!</body> </note> </messages> |
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 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
| <?xml version="1.0" encoding="ISO-8859-1"?><note><to>Tove</to><from>Jani</from><heading>Reminder</heading><body>Don't forget me this weekend!</body></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):
| <?xml version="1.0" encoding="ISO-8859-1"?><!DOCTYPE note SYSTEM "InternalNote.dtd"><note><to>Tove</to><from>Jani</from><heading>Reminder</heading><body>Don't forget me this weekend!</body></note> |
XML DTD
A DTD defines the legal elements of an XML document.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. You can read more about DTD, and how to validate your XML documents in our DTD tutorial.
XML Schema
XML Schema is an XML based alternative to DTD.W3C supports an alternative to DTD called XML Schema. You can read more about XML Schema in our Schema tutorial.
A General XML Validator
To help you check the syntax of your xml files, we have created this link so that you can syntax-check any XML file.XML Errors will Stop you
Errors in XML documents will stop your XML program.The W3C XML specification states that a program should not continue to process an XML document if it finds an error. The reason is that XML software should be easy to write, and that all XML documents should be compatible.
With HTML it was possible to create documents with lots of errors (like when you forget an end tag). One of the main reasons that HTML browsers are so big and incompatible, is that they have their own ways to figure out what a document should look like when they encounter an HTML error.
With XML this should not be possible.
Syntax-check your XML - IE Only
To help you syntax-check your xml, we have used Microsoft's XML parser to create an XML validator.Paste your XML in the text area below, and syntax-check it by pressing the "Validate" button.
<?xml version="1.0" ?> <note> <to>Tove</to> <from>Jani</Ffrom> <heading>Reminder</heading> <body>Don't forget me this weekend!</body> </note>
Syntax-check your XML File - IE Only
You can also syntax-check your XML file by typing the URL of your file into the input field below, and then press the "Validate" buttonFilename:
If you want to syntax-check an error-free XML file, you can paste the following address into the filename field: http://www.w3schools.com/xml/cd_catalog.xml
Note: If you get the error "Access denied" when accessing this file, it is because your Internet Explorer security settings do not allow access across domains! 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 color-coded root and child elements. A plus (+) or minus sign (-) to the left of the elements can be clicked to expand or collapse the element structure. To view the raw XML source (without the + and - signs), select "View Page Source" or "View Source" from the browser menu.
In Netscape 6:
Open the XML file, then right-click in XML file and select "View Page Source". The XML document will then be displayed with color-coded root and child elements.
In Opera 7 and 8:
In Opera 7: Open the XML file, then right-click in XML file and select "Frame" / "View Source". The XML document will be displayed as plain text. In Opera 8: Open the XML file, then right-click in XML file and select "Source". The XML document will be displayed as plain text.
Look at this XML file: note.xml
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.Look at this XML file: note_error.xml
Other XML Examples
Viewing some XML documents will help you get the XML feeling.An XML CD catalog
This is my father's CD collection, stored as XML data (old and boring titles I guess... :-)).
An XML plant catalog
This is a plant catalog from a plant shop, stored as XML data.
A Simple Food Menu
This is a breakfast food menu from a restaurant, stored as XML data.
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 <table> 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 an example of how to use a CSS style sheet to format an XML document:
Take a look at this XML file: The CD catalog
Then look at this style sheet: The CSS file
Finally, view: The CD catalog formatted with the CSS file
Below is a fraction of the XML file. The second line, <?xml-stylesheet type="text/css" href="cd_catalog.css"?>, links the XML file to the CSS file:
| <?xml version="1.0" encoding="ISO-8859-1"?><?xml-stylesheet type="text/css" href="cd_catalog.css"?><CATALOG> <CD> <TITLE>Empire Burlesque</TITLE> <ARTIST>Bob Dylan</ARTIST> <COUNTRY>USA</COUNTRY> <COMPANY>Columbia</COMPANY> <PRICE>10.90</PRICE> <YEAR>1985</YEAR> </CD> <CD> <TITLE>Hide your heart</TITLE> <ARTIST>Bonnie Tyler</ARTIST> <COUNTRY>UK</COUNTRY> <COMPANY>CBS Records</COMPANY> <PRICE>9.90</PRICE> <YEAR>1988</YEAR> </CD>....</CATALOG> |
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!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"):
| <?xml version="1.0" encoding="ISO-8859-1"?><note> <to>Tove</to> <from>Jani</from> <heading>Reminder</heading> <body>Don't forget me this weekend!</body></note> |
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:
| <html><body><xml id="note" src="note.xml"></xml></body></html> |
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
In the next example, we will embed an XML file called "cd_catalog.xml" into an HTML file.View "cd_catalog.xml".
The HTML file looks like this:
| <html><body> <xml id="cdcat" src="cd_catalog.xml"></xml> <table border="1" datasrc="#cdcat"><tr><td><span datafld="ARTIST"></span></td><td><span datafld="TITLE"></span></td></tr></table> </body></html> |
Example explained:
The datasrc attribute of the <table> tag binds the HTML table element to the XML data island. The datasrc attribute refers to the id attribute of the data island.
<td> tags cannot be bound to data, so we are using <span> tags. The <span> tag allows the datafld attribute to refer to the XML element to be displayed. In this case, it is datafld="ARTIST" for the <ARTIST> element and datafld="TITLE" for the <TITLE> element in the XML file. As the XML is read, additional rows are created for each <CD> element.
If you are running IE 5.0 or higher, you can try it yourself.
Also try this example, demonstrating <thead>, <tbody>, and <tfoot>.XML in Real Life
A real-life 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:
| <?xml version="1.0" encoding="ISO-8859-1"?> <nitf> <head><title>Colombia Earthquake</title></head> <body> <headline> <hl1>143 Dead in Colombia Earthquake</hl1></headline><byline> <bytag>By Jared Kotler, Associated Press Writer</bytag></byline><dateline> <location>Bogota, Colombia</location> <date>Monday January 25 1999 7:28 ET</date></dateline> </body> </nitf> |
To read and update, create and manipulate an XML document, you will need an XML parser.
Examples
Parse an XML file - Crossbrowser exampleThis example is a cross-browser example that loads an existing XML document ("note.xml") into the XML parser.
Parse an XML string - Crossbrowser example
This example is a cross-browser example on how to load and parse an XML string.
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.To learn more about the XML DOM, please read our XML DOM tutorial.
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.Microsoft's XML parser supports all the necessary functions to traverse the node tree, access the nodes and their attribute values, insert and delete nodes, and convert the node tree back to XML.
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
Mozilla's XML parser supports all the necessary functions to traverse the node tree, access the nodes and their attribute values, insert and delete nodes, and convert the node tree back to XML.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:| <html><head><script type="text/javascript">var xmlDoc;function loadXML(){// code for IEif (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;}</script></head><body onload="loadXML()"><h1>W3Schools Internal Note</h1><p><b>To:</b> <span id="to"></span><br /><b>From:</b> <span id="from"></span><br /><b>Message:</b> <span id="message"></span></p></body></html> |
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: <from>Jani</from>, the correct syntax is:| getElementsByTagName("from")[0].childNodes[0].nodeValue |
IMPORTANT: getElementsByTagName returns an array of nodes. The array contains all elements with the specified name within the XML document. In this case there is only one "from" element, but you still have to specify the array index ( [0] ).
Parsing an XML String - A Cross browser Example
The following code is a cross-browser example on how to load and parse an XML string:| <html><body><script type="text/javascript">var text="<note>";text=text+"<to>Tove</to>";text=text+"<from>Jani</from>";text=text+"<heading>Reminder</heading>";text=text+"<body>Don't forget me this weekend!</body>";text=text+"</note>";// code for IEif (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 nodevar x=doc.documentElement;document.write("Text of first child element: ");document.write(x.childNodes[0].childNodes[0].nodeValue);document.write("<br />");document.write("Text of second child element: ");document.write(x.childNodes[1].childNodes[0].nodeValue);</script></body></html> |
Output:
| Text of first child element: Tove 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:
| <table> <tr> <td>Apples</td> <td>Bananas</td> </tr></table> |
This XML document carries information about a table (a piece of furniture):
| <table> <name>African Coffee Table</name> <width>80</width> <length>120</length></table> |
If these two XML documents were added together, there would be an element name conflict because both documents contain a <table> element with different content and definition.
Solving Name Conflicts Using a Prefix
This XML document carries information in a table:| <h:table> <h:tr> <h:td>Apples</h:td> <h:td>Bananas</h:td> </h:tr></h:table> |
This XML document carries information about a piece of furniture:
| <f:table> <f:name>African Coffee Table</f:name> <f:width>80</f:width> <f:length>120</f:length></f:table> |
Now there will be no name conflict because the two documents use a different name for their <table> element (<h:table> and <f:table>).
By using a prefix, we have created two different types of <table> elements.
Using Namespaces
This XML document carries information in a table:| <h:table xmlns:h="http://www.w3.org/TR/html4/"> <h:tr> <h:td>Apples</h:td> <h:td>Bananas</h:td> </h:tr></h:table> |
This XML document carries information about a piece of furniture:
| <f:table xmlns:f="http://www.w3schools.com/furniture"> <f:name>African Coffee Table</f:name> <f:width>80</f:width> <f:length>120</f:length></f:table> |
Instead of using only prefixes, we have added an xmlns attribute to the <table> 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:namespace-prefix="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 is to give the namespace a unique name. However, very often companies use the namespace as a pointer to a real Web page containing information about the namespace.
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:
| <table xmlns="http://www.w3.org/TR/html4/"> <tr> <td>Apples</td> <td>Bananas</td> </tr></table> |
This XML document carries information about a piece of furniture:
| <table xmlns="http://www.w3schools.com/furniture"> <name>African Coffee Table</name> <width>80</width> <length>120</length></table> |
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.If you take a close look at the XSL document below, you will see that most of the tags are HTML tags. The tags that are not HTML tags have the prefix xsl, identified by the namespace "http://www.w3.org/1999/XSL/Transform":
| <?xml version="1.0" encoding="ISO-8859-1"?><xsl:stylesheet version="1.0"xmlns:xsl="http://www.w3.org/1999/XSL/Transform"><xsl:template match="/"><html><body> <h2>My CD Collection</h2> <table border="1"> <tr> <th align="left">Title</th> <th align="left">Artist</th> </tr> <xsl:for-each select="catalog/cd"> <tr> <td><xsl:value-of select="title"/></td> <td><xsl:value-of select="artist"/></td> </tr> </xsl:for-each> </table></body></html></xsl:template></xsl:stylesheet> |
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</message> |
The parser does this because XML elements can contain other elements, as in this example, where the <name> element contains two other elements (first and last):
| <name><first>Bill</first><last>Gates</last></name> |
and the parser will break it up into sub-elements like this:
| <name> <first>Bill</first> <last>Gates</last></name> |
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</message> |
To avoid this, you have to replace the "<" character with an entity reference, like this:
| <message>if salary < 1000 then</message> |
There are 5 predefined entity references in XML:
| < | < | less than |
| > | > | greater than |
| & | & | ampersand |
| ' | ' | apostrophe |
| " | " | quotation mark |
Note: Only the characters "<" and "&" are strictly illegal in XML. Apostrophes, quotation marks and greater than signs are legal, but it is a good habit to replace them.
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 "<![CDATA[" and ends with "]]>":
| <script><![CDATA[function matchwo(a,b){if (a < b && a < 0) then { return 1 }else { return 0 }}]]></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.Also make sure there are no spaces or line breaks inside the "]]>" string. 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):
| <?xml version="1.0"?><note> <from>Jani</from> <to>Tove</to> <message>Norwegian: æøå. French: êèé</message></note> |
The file above, note_encode_none_u.xml 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 "UTF-16" encoding.If you add an encoding attribute to XML files saved as Unicode, windows encoding values will generate an error.
The following encoding (open it), will NOT give an error message:
| <?xml version="1.0" encoding="windows-1252"?> |
The following encoding (open it), will NOT give an error message:
| <?xml version="1.0" encoding="ISO-8859-1"?> |
The following encoding (open it), will NOT give an error message:
| <?xml version="1.0" encoding="UTF-8"?> |
The following encoding (open it), will NOT generate an error in IE 5+, Firefox, or Opera, but it WILL generate an error in Netscape 6.2.
| <?xml version="1.0" encoding="UTF-16"?> |
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 single-byte 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/UTF-16 but the encoding attribute specified a single-byte encoding like Windows-1252, ISO-8859-1 or UTF-8. You can also get this error message if your document was saved with single-byte encoding, but the encoding attribute specified a double-byte encoding like UTF-16.
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 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:
| <?xml version="1.0" encoding="ISO-8859-1"?><note> <from>Jani</from> <to>Tove</to> <message>Remember me this weekend</message></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("<?xml version='1.0' encoding='ISO-8859-1'?>")response.Write("<note>")response.Write("<from>Jani</from>")response.Write("<to>Tove</to>")response.Write("<message>Remember me this weekend</message>")response.Write("</note>")%> |
Note that the content type of the response must be set to "text/xml".
See how the ASP file will be returned from the server.
If you don't know how to write ASP, please visit our ASP tutorial
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"set conn=Server.CreateObject("ADODB.Connection") 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("<?xml version='1.0' encoding='ISO-8859-1'?>")response.write("<guestbook>")while (not rs.EOF) response.write("<guest>") response.write("<fname>" & rs("fname") & "</fname>") response.write("<lname>" & rs("lname") & "</lname>") response.write("</guest>") rs.MoveNext()wendrs.close()conn.close()response.write("</guestbook>")%> |
See the real life database output from the ASP file above.
The example above uses ASP with ADO. If you don't know how to use ADO, please visit our ADO tutorial.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:| <?xml version="1.0" encoding="ISO-8859-1"?><CATALOG> <CD> <TITLE>Empire Burlesque</TITLE> <ARTIST>Bob Dylan</ARTIST> <COUNTRY>USA</COUNTRY> <COMPANY>Columbia</COMPANY> <PRICE>10.90</PRICE> <YEAR>1985</YEAR> </CD>..... more .... |
View the full "cd_catalog.xml" file in your browser.
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"></xml> |
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:
| <table datasrc="#xmldso" width="100%" border="1"><thead><th>Title</th><th>Artist</th><th>Year</th></thead><tr align="left"><td><span datafld="TITLE"></span></td><td><span datafld="ARTIST"></span></td><td><span datafld="YEAR"></span></td></tr></table> |
If you have IE 5.0 or higher: See how the XML data is displayed inside an HTML table.
Bind the Data Island to <span> or <div> Elements
<span> or <div> 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 <div> 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:
| <br />Title:<span datasrc="#xmldso" datafld="TITLE"></span><br />Artist:<span datasrc="#xmldso" datafld="ARTIST"></span> |