** pic_xml In our XML tutorial you will learn what XML is and the difference between XML and HTML. You will also learn how to start using XML in your applications.
**

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 some basic understanding of the following:

WWW, HTML and the basics of building Web pages
Web scripting languages like JavaScript or VBScript

If you want to study these subjects first, before you start reading about XML, you can find the tutorials you need at W3Schools' Home Page .

What is XML?

XML stands for E X tensible M arkup L anguage
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

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:

1<note>
2<to>Tove</to>
3<from>Jani</from>
4<heading>Reminder</heading>
5<body>Don't forget me this weekend!</body>
6</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

   1<p>, <h1>, etc.). 
   2
   3XML allows the author to define his own tags and his own document structure. 
   4
   5The 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. 
   6
   7* * *
   8
   9##  XML is a complement to HTML 
  10
  11**XML is not a replacement for HTML.**
  12
  13It 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. 
  14
  15My best description of XML is this: **XML is a cross-platform, software and hardware independent tool for transmitting information.**
  16
  17* * *
  18
  19##  XML in future Web development 
  20
  21**XML is going to be everywhere.**
  22
  23We 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. 
  24
  25We 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. 
  26
  27* * *
  28
  29##  XML Joke 
  30
  31Question: When should I use XML? 
  32
  33Answer: When you need a buzzword in your resume. 
  34
  35* * *
  36
  37  
  38
  39
  40#  How can XML be Used? 
  41
  42![back](http://www.w3schools.com/images/btn_previous.gif) ![next](http://www.w3schools.com/images/btn_next.gif)
  43
  44* * *
  45
  46It is important to understand that XML was designed to store, carry, and exchange data. XML was not designed to display data. 
  47
  48* * *
  49
  50##  XML can Separate Data from HTML 
  51
  52**With XML, your data is stored outside your HTML.**
  53
  54When 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. 
  55
  56XML 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. 
  57
  58* * *
  59
  60##  XML is used to Exchange Data 
  61
  62**With XML, data can be exchanged between incompatible systems.**
  63
  64In 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. 
  65
  66Converting the data to XML can greatly reduce this complexity and create data that can be read by many different types of applications. 
  67
  68* * *
  69
  70##  XML and B2B 
  71
  72**With XML, financial information can be exchanged over the Internet.**
  73
  74Expect to see a lot about XML and B2B (Business To Business) in the near future. 
  75
  76XML 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. 
  77
  78* * *
  79
  80##  XML can be used to Share Data 
  81
  82**With XML, plain text files can be used to share data.**
  83
  84Since XML data is stored in plain text format, XML provides a software- and hardware-independent way of sharing data. 
  85
  86This 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. 
  87
  88* * *
  89
  90##  XML can be used to Store Data 
  91
  92**With XML, plain text files can be used to store data.**
  93
  94XML 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. 
  95
  96* * *
  97
  98##  XML can make your Data more Useful 
  99
 100**With XML, your data is available to more users.**
 101
 102Since XML is independent of hardware, software and application, you can make your data available to other than only standard HTML browsers. 
 103
 104Other 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. 
 105
 106* * *
 107
 108##  XML can be used to Create new Languages 
 109
 110**XML is the mother of WAP and WML.**
 111
 112The Wireless Markup Language (WML), used to markup Internet applications for handheld devices like mobile phones, is written in XML. 
 113
 114You can read more about WML in our  WML tutorial  . 
 115
 116* * *
 117
 118##  If Developers have Sense 
 119
 120**If they DO have sense, all future applications will exchange their data in XML.**
 121
 122The 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. 
 123
 124We can only pray that Microsoft and all the other software vendors will agree. 
 125
 126* * *
 127
 128  
 129
 130
 131#  XML Syntax 
 132
 133![back](http://www.w3schools.com/images/btn_previous.gif) ![next](http://www.w3schools.com/images/btn_next.gif)
 134
 135* * *
 136
 137The syntax rules of XML are very simple and very strict. The rules are very easy to learn, and very easy to use. 
 138
 139Because of this, creating software that can read and manipulate XML is very easy to do. 
 140
 141* * *
 142
 143##  An example XML document 
 144
 145**XML documents use a self-describing and simple syntax.**
 146    
 147    
 148    <?xml version="1.0" encoding="ISO-8859-1"?>
 149<note>
 150<to>Tove</to>
 151<from>Jani</from>
 152<heading>Reminder</heading>
 153<body>Don't forget me this weekend!</body>
 154</note>  
 155  
 156---  
 157  
 158The 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. 
 159
 160The next line describes the root element of the document (like it was saying: "this document is a note"): 
 161    
 162    
 163    <note>  
 164  
 165---  
 166  
 167The next 4 lines describe 4 child elements of the root (to, from, heading, and body): 
 168    
 169    
 170    <to>Tove</to>
 171<from>Jani</from>
 172<heading>Reminder</heading>
 173<body>Don't forget me this weekend!</body>  
 174  
 175---  
 176  
 177And finally the last line defines the end of the root element: 
 178    
 179    
 180    </note>  
 181  
 182---  
 183  
 184Can 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? 
 185
 186* * *
 187
 188##  All XML elements must have a closing tag 
 189
 190**With XML, it is illegal to omit the closing tag.**
 191
 192In HTML some elements do not have to have a closing tag. The following code is legal in HTML: 
 193    
 194    
 195    <p>This is a paragraph
 196    <p>This is another paragraph  
 197  
 198---  
 199  
 200In XML all elements must have a closing tag, like this: 
 201    
 202    
 203    <p>This is a paragraph</p>
 204<p>This is another paragraph</p>   
 205  
 206---  
 207  
 208**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. 
 209
 210* * *
 211
 212##  XML tags are case sensitive 
 213
 214**Unlike HTML, XML tags are case sensitive.**
 215
 216With XML, the tag <letter> is different from the tag <letter>. 
 217
 218Opening and closing tags must therefore be written with the same case: 
 219    
 220    
 221    <message>This is incorrect</message>
 222<message>This is correct</message>  
 223  
 224---  
 225  
 226
 227
 228* * *
 229
 230##  All XML elements must be properly nested 
 231
 232**Improper nesting of tags makes no sense to XML.**
 233
 234In HTML some elements can be improperly nested within each other like this: 
 235    
 236    
 237    <b><i>This text is bold and italic</i></b>  
 238  
 239---  
 240  
 241In XML all elements must be properly nested within each other like this: 
 242    
 243    
 244    <b><i>This text is bold and italic</i></b>  
 245  
 246---  
 247  
 248
 249
 250* * *
 251
 252##  All XML documents must have a root element 
 253
 254**All XML documents must contain a single tag pair to define a root element.**
 255
 256All other elements must be within this root element. 
 257
 258All elements can have sub elements (child elements). Sub elements must be correctly nested within their parent element: 
 259    
 260    
 261    <root>
 262<child>
 263<subchild>.....</subchild>
 264</child>
 265</root>   
 266  
 267---  
 268  
 269
 270
 271* * *
 272
 273##  Attribute values must always be quoted 
 274
 275**With XML, it is illegal to omit quotation marks around attribute values.**
 276
 277XML 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: 
 278    
 279    
 280    <?xml version="1.0" encoding="ISO-8859-1"?>
 281<note date="12/11/2002">
 282<to>Tove</to>
 283<from>Jani</from>
 284</note>  
 285  
 286---  
 287  
 288
 289    
 290    
 291    <?xml version="1.0" encoding="ISO-8859-1"?>
 292<note date="12/11/2002">
 293<to>Tove</to>
 294<from>Jani</from>
 295</note>  
 296  
 297---  
 298  
 299The error in the first document is that the date attribute in the note element is not quoted. 
 300
 301This is correct: date="12/11/2002". This is incorrect: date=12/11/2002. 
 302
 303* * *
 304
 305##  With XML, white space is preserved 
 306
 307**With XML, the white space in your document is not truncated** . 
 308
 309This is unlike HTML. With HTML, a sentence like this: 
 310
 311Hello my name is Tove, 
 312
 313will be displayed like this: 
 314
 315Hello my name is Tove, 
 316
 317because HTML reduces multiple, consecutive white space characters to a single white space. 
 318
 319* * *
 320
 321##  With XML, CR / LF is converted to LF 
 322
 323**With XML, a new line is always stored as LF** . 
 324
 325Do you know what a typewriter is? Well, a typewriter is a mechanical device which was used last century to produce printed documents. :-) 
 326
 327After 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. 
 328
 329In 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. 
 330
 331* * *
 332
 333##  Comments in XML 
 334
 335The syntax for writing comments in XML is similar to that of HTML. 
 336
 337<!-- This is a comment -->
 338
 339* * *
 340
 341##  There is nothing special about XML 
 342
 343There is nothing special about XML. It is just plain text with the addition of some XML tags enclosed in angle brackets. 
 344
 345Software 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. 
 346
 347In 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. 
 348
 349* * *
 350
 351  
 352
 353
 354#  XML Elements 
 355
 356![back](http://www.w3schools.com/images/btn_previous.gif) ![next](http://www.w3schools.com/images/btn_next.gif)
 357
 358* * *
 359
 360XML Elements are extensible and they have relationships. 
 361
 362XML Elements have simple naming rules. 
 363
 364* * *
 365
 366##  XML Elements are Extensible 
 367
 368**XML documents can be extended to carry more information.**
 369
 370Look at the following XML NOTE example: 
 371    
 372    
 373    <note>
 374<to>Tove</to>
 375<from>Jani</from>
 376<body>Don't forget me this weekend!</body>
 377</note>  
 378  
 379---  
 380  
 381Let's imagine that we created an application that extracted the <to>, <from>, and <body> elements from the XML document to produce this output: 
 382
 383**MESSAGE**
 384
 385**To:** Tove   
 386**From:** Jani 
 387
 388Don't forget me this weekend!   
 389  
 390---  
 391  
 392Imagine that the author of the XML document added some extra information to it: 
 393    
 394    
 395    <note>
 396<date>2002-08-01</date>
 397<to>Tove</to>
 398<from>Jani</from>
 399<heading>Reminder</heading>
 400<body>Don't forget me this weekend!</body>
 401</note>  
 402  
 403---  
 404  
 405Should the application break or crash? 
 406
 407No. The application should still be able to find the <to>, <from>, and <body> elements in the XML document and produce the same output. 
 408
 409**XML documents are E** **xtensible.**
 410
 411* * *
 412
 413##  XML Elements have Relationships 
 414
 415**Elements are related as parents and children.**
 416
 417To understand XML terminology, you have to know how relationships between XML elements are named, and how element content is described. 
 418
 419Imagine that this is a description of a book: 
 420
 421**My First XML**
 422
 423Introduction to XML 
 424
 425  * What is HTML 
 426  * What is XML 
 427
 428
 429
 430XML Syntax 
 431
 432  * Elements must have a closing tag 
 433  * Elements must be properly nested 
 434
 435  
 436---  
 437  
 438Imagine that this XML document describes the book: 
 439    
 440    
 441    <book>
 442<title>My First XML</title>
 443<prod id="33-657" media="paper"></prod>
 444<chapter>Introduction to XML
 445    <para>What is HTML</para>
 446<para>What is XML</para>
 447</chapter>
 448<chapter>XML Syntax
 449    <para>Elements must have a closing tag</para>
 450<para>Elements must be properly nested</para>
 451</chapter>
 452</book>  
 453  
 454---  
 455  
 456Book 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. 
 457
 458* * *
 459
 460##  Elements have Content 
 461
 462**Elements can have different content types.**
 463
 464An **XML element** is everything from (including) the element's start tag to (including) the element's end tag. 
 465
 466An element can have **element** content, **mixed** content, **simple** content, or **empty** content. An element can also have **attributes** . 
 467
 468In 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. 
 469
 470In 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". 
 471
 472* * *
 473
 474##  Element Naming 
 475
 476**XML elements must follow these naming rules:**
 477
 478  * Names can contain letters, numbers, and other characters 
 479  * Names must not start with a number or punctuation character 
 480  * Names must not start with the letters xml (or XML or Xml ..) 
 481  * Names cannot contain spaces 
 482
 483
 484
 485Take care when you "invent" element names and follow these simple rules: 
 486
 487Any name can be used, no words are reserved, but the idea is to make names descriptive. Names with an underscore separator are nice. 
 488
 489Examples: <first_name>, <last_name>. 
 490
 491Avoid "-" 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." 
 492
 493Element 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>. 
 494
 495XML 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. 
 496
 497Non-English letters like éòá are perfectly legal in XML element names, but watch out for problems if your software vendor doesn't support them. 
 498
 499The ":" should not be used in element names because it is reserved to be used for something called namespaces (more later). 
 500
 501* * *
 502
 503  
 504
 505
 506#  XML Attributes 
 507
 508![back](http://www.w3schools.com/images/btn_previous.gif) ![next](http://www.w3schools.com/images/btn_next.gif)
 509
 510* * *
 511
 512XML elements can have attributes in the start tag, just like HTML. 
 513
 514Attributes are used to provide additional information about elements. 
 515
 516* * *
 517
 518##  XML Attributes 
 519
 520**XML elements can have attributes.**
 521
 522From HTML you will remember this: <img src="computer.gif"/>. The SRC attribute provides additional information about the IMG element. 
 523
 524In HTML (and in XML) attributes provide additional information about elements: 
 525    
 526    
 527    <img src="computer.gif"/>
 528<a href="demo.asp">  
 529  
 530---  
 531  
 532Attributes 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: 
 533    
 534    
 535    <file type="gif">computer.gif</file>  
 536  
 537---  
 538  
 539
 540
 541* * *
 542
 543##  Quote Styles, "female" or 'female'? 
 544
 545Attribute 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: 
 546    
 547    
 548    <person sex="female">  
 549  
 550---  
 551  
 552or like this: 
 553    
 554    
 555    <person sex="female">  
 556  
 557---  
 558  
 559**Note:** If the attribute value itself contains double quotes it is necessary to use single quotes, like in this example: 
 560    
 561    
 562    <gangster name='George "Shotgun" Ziegler'>  
 563  
 564---  
 565  
 566**Note:** If the attribute value itself contains single quotes it is necessary to use double quotes, like in this example: 
 567    
 568    
 569    <gangster name="George 'Shotgun' Ziegler">  
 570  
 571---  
 572  
 573
 574
 575* * *
 576
 577##  Use of Elements vs. Attributes 
 578
 579**Data can be stored in child elements or in attributes.**
 580
 581Take a look at these examples: 
 582    
 583    
 584    <person sex="female">
 585<firstname>Anna</firstname>
 586<lastname>Smith</lastname>
 587</person>  
 588  
 589---  
 590  
 591
 592    
 593    
 594    <person>
 595<sex>female</sex>
 596<firstname>Anna</firstname>
 597<lastname>Smith</lastname>
 598</person>  
 599  
 600---  
 601  
 602In the first example sex is an attribute. In the last, sex is a child element. Both examples provide the same information. 
 603
 604There 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. 
 605
 606* * *
 607
 608##  My Favorite Way 
 609
 610**I like to store data in child elements.**
 611
 612The following three XML documents contain exactly the same information: 
 613
 614A date attribute is used in the first example: 
 615    
 616    
 617    <note date="12/11/2002">
 618<to>Tove</to>
 619<from>Jani</from>
 620<heading>Reminder</heading>
 621<body>Don't forget me this weekend!</body>
 622</note>  
 623  
 624---  
 625  
 626A date element is used in the second example: 
 627    
 628    
 629    <note>
 630<date>12/11/2002</date>
 631<to>Tove</to>
 632<from>Jani</from>
 633<heading>Reminder</heading>
 634<body>Don't forget me this weekend!</body>
 635</note>  
 636  
 637---  
 638  
 639An expanded date element is used in the third: (THIS IS MY FAVORITE): 
 640    
 641    
 642    <note>
 643<date>
 644<day>12</day>
 645<month>11</month>
 646<year>2002</year>
 647</date>
 648<to>Tove</to>
 649<from>Jani</from>
 650<heading>Reminder</heading>
 651<body>Don't forget me this weekend!</body>
 652</note>   
 653  
 654---  
 655  
 656
 657
 658* * *
 659
 660##  Avoid using attributes? 
 661
 662**Should you avoid using attributes?**
 663
 664Some of the problems with using attributes are: 
 665
 666  * attributes cannot contain multiple values (child elements can) 
 667  * attributes are not easily expandable (for future changes) 
 668  * attributes cannot describe structures (child elements can) 
 669  * attributes are more difficult to manipulate by program code 
 670  * 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 
 671
 672
 673
 674If 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. 
 675
 676Don't end up like this ( if you think this looks like XML, you have not understood the point): 
 677    
 678    
 679    <note body="Don't forget me this weekend!" day="12" from="Jani" heading="Reminder" month="11" to="Tove" year="2002">
 680</note>   
 681  
 682---  
 683  
 684
 685
 686* * *
 687
 688##  An Exception to my Attribute rule 
 689
 690**Rules always have exceptions.**
 691
 692My rule about attributes has one exception: 
 693
 694Sometimes 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: 
 695    
 696    
 697    <messages>
 698<note id="p501">
 699<to>Tove</to>
 700<from>Jani</from>
 701<heading>Reminder</heading>
 702<body>Don't forget me this weekend!</body>
 703</note>
 704<note id="p502">
 705<to>Jani</to>
 706<from>Tove</from>
 707<heading>Re: Reminder</heading>
 708<body>I will not!</body>
 709</note>
 710</messages>  
 711  
 712---  
 713  
 714The 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. 
 715
 716What 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. 
 717
 718* * *
 719
 720  
 721
 722
 723#  XML Validation 
 724
 725![back](http://www.w3schools.com/images/btn_previous.gif) ![next](http://www.w3schools.com/images/btn_next.gif)
 726
 727* * *
 728
 729XML with correct syntax is Well Formed XML. 
 730
 731XML validated against a DTD is Valid XML. 
 732
 733* * *
 734
 735##  "Well Formed" XML documents 
 736
 737**A "Well Formed" XML document has correct XML syntax.**
 738
 739A "Well Formed" XML document is a document that conforms to the XML syntax rules that were described in the previous chapters: 
 740    
 741    
 742    <?xml version="1.0" encoding="ISO-8859-1"?>
 743<note>
 744<to>Tove</to>
 745<from>Jani</from>
 746<heading>Reminder</heading>
 747<body>Don't forget me this weekend!</body>
 748</note>  
 749  
 750---  
 751  
 752
 753
 754* * *
 755
 756##  "Valid" XML documents 
 757
 758**A "Valid" XML document also conforms to a DTD.**
 759
 760A "Valid" XML document is a "Well Formed" XML document, which also conforms to the rules of a Document Type Definition (DTD): 
 761    
 762    
 763    <?xml version="1.0" encoding="ISO-8859-1"?>
 764<!DOCTYPE note SYSTEM "InternalNote.dtd">
 765
 766<note>
 767<to>Tove</to>
 768<from>Jani</from>
 769<heading>Reminder</heading>
 770<body>Don't forget me this weekend!</body>
 771</note>   
 772  
 773---  
 774  
 775
 776
 777* * *
 778
 779##  XML DTD 
 780
 781**A DTD defines the legal elements of an XML document.**
 782
 783The 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  . 
 784
 785* * *
 786
 787##  XML Schema 
 788
 789**XML Schema is an XML based alternative to DTD.**
 790
 791W3C supports an alternative to DTD called XML Schema. You can read more about XML Schema in our  Schema tutorial  . 
 792
 793* * *
 794
 795##  Errors will Stop you 
 796
 797**Errors in XML documents will stop the XML program.**
 798
 799The W3C XML specification states that a program should not continue to process an XML document if it finds a validation error. The reason is that XML software should be easy to write, and that all XML documents should be compatible. 
 800
 801With 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. 
 802
 803With XML this should not be possible. 
 804
 805* * *
 806
 807##  A general XML Validator 
 808
 809To help you validate your xml files, we have created this link so that you can  Validate any XML file  . 
 810
 811* * *
 812
 813  
 814
 815
 816#  XML Browser Support 
 817
 818![prev](http://www.w3schools.com/images/btn_previous.gif) ![next](http://www.w3schools.com/images/btn_next.gif)
 819
 820* * *
 821
 822In our XML tutorial we have focused on Internet Explorer 5.0+. 
 823
 824* * *
 825
 826##  XML on this Web Site 
 827
 828**Many browsers support XML. We are focusing on Internet Explorer 5.0+.**
 829
 830Some of you have complained about this, but we think this is the most practical way to demonstrate real XML examples for you over the Internet. 
 831
 832* * *
 833
 834##  XML in Mozilla Firefox 1.0 
 835
 836Mozilla Firefox 1.0 supports the XML 1.0 standard. 
 837
 838* * *
 839
 840##  XML in Netscape 6 
 841
 842Netscape 6 supports XML. 
 843
 844To look at the XML source in Netscape 6: right-click on the page and select "View Page Source". 
 845
 846* * *
 847
 848##  XML in Internet Explorer 5.0 
 849
 850Internet Explorer 5.0 supports the XML 1.0 standard. 
 851
 852Internet Explorer 5.0 supports most of the international standards for XML 1.0 and the XML DOM (Document Object Model). These standards are set by the World Wide Web Consortium (W3C). 
 853
 854Internet Explorer 5.0 has the following XML support: 
 855
 856  * Viewing of XML documents 
 857  * Full support for W3C DTD standards 
 858  * XML embedded in HTML as Data Islands 
 859  * Binding XML data to HTML elements 
 860  * Transforming and displaying XML with XSL 
 861  * Displaying XML with CSS 
 862  * Access to the XML DOM 
 863
 864
 865
 866Internet Explorer 5.0 also has support for Behaviors: 
 867
 868  * Behaviors is a Microsoft-only technology 
 869  * Behaviors can separate scripts from an HTML page. 
 870  * Behaviors can store XML data on the client's disk. 
 871
 872
 873
 874Examples of all these features are given in the next chapters of this web site. 
 875
 876* * *
 877
 878  
 879
 880
 881#  Viewing XML Files 
 882
 883![prev](http://www.w3schools.com/images/btn_previous.gif) ![next](http://www.w3schools.com/images/btn_next.gif)
 884
 885* * *
 886
 887Raw XML files can be viewed in Mozilla Firefox, IE 5.0+ and in Netscape 6. 
 888
 889However, to make XML documents to display like nice web pages, you will have to add some display information. 
 890
 891* * *
 892
 893##  Viewing XML Files 
 894
 895**In Mozilla Firefox and IE 5.0+:**
 896
 897Click on a link to an XML file, type the direct URL in the address bar, or double-click on the name of an XML file in a folder. 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. 
 898
 899**In Netscape 6:**
 900
 901Open the XML file (via a link or URL), 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. 
 902
 903Look at this XML file:  note.xml 
 904
 905**Note: Do not expect XML files to be formatted like HTML documents!**
 906
 907* * *
 908
 909##  Viewing an Invalid XML File 
 910
 911If an erroneous XML file is opened, the browser will report the error. 
 912
 913Look at this XML file:  note_error.xml 
 914
 915* * *
 916
 917##  Other XML Examples 
 918
 919Viewing some XML documents will help you get the XML feeling. 
 920
 921An XML CD catalog    
 922This is my father's CD collection, stored as XML data (old and boring titles I think.... :-)). 
 923
 924An XML plant catalog    
 925This is a plant catalog from a plant shop, stored as XML data. 
 926
 927A Simple Food Menu    
 928This is a breakfast food menu from a restaurant, stored as XML data. 
 929
 930* * *
 931
 932##  Why does XML display like this? 
 933
 934XML documents do not carry information about how to display the data. 
 935
 936Since 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. 
 937
 938Without any information about how to display the data, most browsers will just display the XML document as it is. 
 939
 940In the next chapters, we will take a look at different solutions to the display problem, using CSS, XSL, JavaScript, and XML Data Islands. 
 941
 942* * *
 943
 944  
 945
 946
 947#  Displaying XML with CSS 
 948
 949![back](http://www.w3schools.com/images/btn_previous.gif) ![next](http://www.w3schools.com/images/btn_next.gif)
 950
 951* * *
 952
 953With CSS (Cascading Style Sheets) you can add display information to an XML document. 
 954
 955* * *
 956
 957##  Displaying your future XML files with CSS? 
 958
 959Would you use CSS to format your future XML files? No, we don't think so! But we could not resist giving it a try: 
 960
 961Take a look at this XML file:  The CD catalog 
 962
 963Then look at this style sheet:  The CSS file 
 964
 965Finally, view:  The CD catalog formatted with the CSS file 
 966
 967Below 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: 
 968    
 969    
 970    <?xml version="1.0" encoding="ISO-8859-1"?>
 971<?xml-stylesheet type="text/css" href="cd_catalog.css"?>
 972<catalog>
 973<cd>
 974<title>Empire Burlesque</title>
 975<artist>Bob Dylan</artist>
 976<country>USA</country>
 977<company>Columbia</company>
 978<price>10.90</price>
 979<year>1985</year>
 980</cd>
 981<cd>
 982<title>Hide your heart</title>
 983<artist>Bonnie Tyler</artist>
 984<country>UK</country>
 985<company>CBS Records</company>
 986<price>9.90</price>
 987<year>1988</year>
 988</cd>
 989    .
 990    .
 991    .
 992    .
 993    </catalog>     
 994  
 995---  
 996  
 997We DO NOT believe that formatting XML with CSS is the future of the Web. Even if it looks right to use CSS this way, we DO believe that formatting with XSL will be the new standard (as soon as all main browsers support it). 
 998
 999* * *
1000
1001##  Creating your future Homepages with XML? 
1002
1003Will you be writing your future Homepages in XML? No, we don't think you will! But we could not resist giving it a try :  A homepage written in XML  . 
1004
1005We DO NOT believe that XML will be used to create future Homepages. 
1006
1007* * *
1008
1009  
1010
1011
1012#  Displaying XML with XSL 
1013
1014![back](http://www.w3schools.com/images/btn_previous.gif) ![next](http://www.w3schools.com/images/btn_next.gif)
1015
1016* * *
1017
1018With XSL you can add display information to your XML document. 
1019
1020* * *
1021
1022##  Displaying XML with XSL 
1023
1024**XSL is the preferred style sheet language of XML.**
1025
1026XSL (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: 
1027
1028If you have Netscape 6 or IE 5 or higher you can view  the XML file  and  the XSL style sheet  . 
1029
1030View the result in IE 6 
1031
1032View the result in IE 5 
1033
1034Below is a fraction of the XML file, with an added XSL reference. The second line, ** <?xml-stylesheet type="text/xsl" href="simple.xsl"?> ** , links the XML file to the XSL file: 
1035    
1036    
1037    <?xml version="1.0" encoding="ISO-8859-1"?>
1038<?xml-stylesheet type="text/xsl" href="simple.xsl"?>
1039<breakfast_menu>
1040<food>
1041<name>Belgian Waffles</name>
1042<price>$5.95</price>
1043<description>
1044           two of our famous Belgian Waffles
1045        </description>
1046<calories>650</calories>
1047</food>
1048</breakfast_menu>  
1049  
1050---  
1051  
1052If you want to learn more about XSL, please visit our  XSL tutorial  . 
1053
1054* * *
1055
1056  
1057
1058
1059#  XML in Data Islands 
1060
1061![prev](http://www.w3schools.com/images/btn_previous.gif) ![next](http://www.w3schools.com/images/btn_next.gif)
1062
1063* * *
1064
1065With Internet Explorer 5.0 and higher, XML can be embedded within HTML pages in Data Islands. 
1066
1067* * *
1068
1069##  XML Embedded in HTML 
1070
1071**The unofficial <xml> tag is used to embed XML data within HTML. **
1072
1073XML data can be embedded directly in an HTML page like this: 
1074    
1075    
1076    <xml id="note">
1077<note>
1078<to>Tove</to>
1079<from>Jani</from>
1080<heading>Reminder</heading>
1081<body>Don't forget me this weekend!</body>
1082</note>
1083</xml>  
1084  
1085---  
1086  
1087Or a separate XML file can be embedded like this: 
1088    
1089    
1090    <xml id="note" src="note.xml">
1091</xml>  
1092  
1093---  
1094  
1095**Note that the <xml> tag is an HTML element, not an XML element. **
1096
1097* * *
1098
1099##  Data Binding 
1100
1101**Data Islands can be bound to HTML elements (like HTML tables).**
1102
1103In the example below, an XML Data Island with an ID "cdcat" is loaded from an external XML file. An HTML table is bound to the Data Island with a data source attribute, and finally the tabledata elements are bound to the XML data with a data field attribute inside a span. 
1104    
1105    
1106    <html>
1107<body>
1108<xml id="cdcat" src="cd_catalog.xml"></xml>
1109<table border="1" datasrc="#cdcat">
1110<tr>
1111<td><span datafld="ARTIST"></span></td>
1112<td><span datafld="TITLE"></span></td>
1113</tr>
1114</table>
1115</body>
1116</html>  
1117  
1118---  
1119  
1120If you are running IE 5.0 or higher, you can  try it yourself  . 
1121
1122With IE 5.0 and higher you can also view the  external XML file  . 
1123
1124Also try  this example  , demonstrating <thead>, <tbody>, and <tfoot>. 
1125
1126* * *
1127
1128  
1129
1130
1131#  The Microsoft XML Parser 
1132
1133![prev](http://www.w3schools.com/images/btn_previous.gif) ![next](http://www.w3schools.com/images/btn_next.gif)
1134
1135* * *
1136
1137To read and update - create and manipulate - an XML document, you need an XML parser. 
1138
1139* * *
1140
1141##  Using the XML parser 
1142
1143**The Microsoft XML parser comes with Microsoft Internet Explorer 5.0.**
1144
1145Once you have installed IE 5.0, the parser is available to scripts, both inside HTML documents and inside ASP files. The parser features a language-neutral programming model that supports: 
1146
1147  * JavaScript, VBScript, Perl, VB, Java, C++ and more 
1148  * W3C XML 1.0 and XML DOM 
1149  * DTD and validation 
1150
1151
1152
1153If you are using JavaScript in IE 5.0, you can create an XML document object with the following code: 
1154    
1155    
1156    var xmlDoc=new ActiveXObject("Microsoft.XMLDOM")  
1157  
1158---  
1159  
1160If you are using VBScript, you create the XML document object with the following code: 
1161    
1162    
1163    set xmlDoc=CreateObject("Microsoft.XMLDOM")  
1164  
1165---  
1166  
1167If you are using VBScript in ASP, you can use the following code: 
1168    
1169    
1170    set xmlDoc=Server.CreateObject("Microsoft.XMLDOM")  
1171  
1172---  
1173  
1174
1175
1176* * *
1177
1178##  Loading an XML file into the parser 
1179
1180**XML files can be loaded into the parser using script code.**
1181
1182The following code loads an XML document (note.xml) into the XML parser: 
1183    
1184    
1185    <script type="text/javascript">
1186    var xmlDoc = new ActiveXObject("Microsoft.XMLDOM")
1187    xmlDoc.async="false"
1188    xmlDoc.load("note.xml")
1189    // ....... processing the document goes here
1190    </script>  
1191  
1192---  
1193  
1194The second line in the code above creates an instance of the Microsoft XML parser. 
1195
1196The third line turns off asynchronized loading, to make sure that the parser will not continue execution before the document is fully loaded. 
1197
1198The fourth line tells the parser to load the XML document called note.xml. 
1199
1200* * *
1201
1202##  Loading pure XML text into the parser 
1203
1204**XML text can also be loaded from a text string.**
1205
1206The following code loads a text string into the XML parser: 
1207    
1208    
1209    <script type="text/javascript">
1210    
1211    var text="<note>"
1212    text=text+"<to>Tove</to><from>Jani</from>"
1213    text=text+"<heading>Reminder</heading>"
1214    text=text+"<body>Don't forget me this weekend!</body>"
1215    text=text+"</note>"
1216    
1217    var xmlDoc = new ActiveXObject("Microsoft.XMLDOM")
1218    xmlDoc.async="false"
1219    xmlDoc.loadXML(text)
1220    // ....... processing the document goes here
1221    </script>  
1222  
1223---  
1224  
1225Note that the "loadXML" method (instead of the "load" method) is used to load a text string. 
1226
1227* * *
1228
1229##  Displaying XML with JavaScript 
1230
1231**To display XML you can use JavaScript.**
1232
1233JavaScript (or VBScript) can be used to import data from an XML file and display the XML data inside an HTML page. 
1234
1235To see how XML and HTML complement each other this way; first look at the **XML** document (  note.xml  ), then open the **HTML** document (  note.htm  ) that contains a JavaScript which reads the XML file and displays the information inside predefined spans in the HTML page. 
1236
1237To see how it works,  Try It Yourself 
1238
1239You can see a lot more of this kind of JavaScript in our  DOM School  . 
1240
1241* * *
1242
1243  
1244
1245
1246#  XML in Real Life 
1247
1248![back](http://www.w3schools.com/images/btn_previous.gif) ![next](http://www.w3schools.com/images/btn_next.gif)
1249
1250* * *
1251
1252Some real-life examples of how XML can be used to carry information. 
1253
1254* * *
1255
1256##  Example: XML News 
1257
1258**XMLNews is a specification for exchanging news and other information.**
1259
1260Using 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. 
1261
1262* * *
1263
1264##  An example XML News document: 
1265    
1266    
1267    <?xml version="1.0" encoding="ISO-8859-1"?>
1268<nitf>
1269<head>
1270<title>Colombia Earthquake</title>
1271</head>
1272<body>
1273<body.head>
1274<headline>
1275<hl1>143 Dead in Colombia Earthquake</hl1>
1276</headline>
1277<byline>
1278<bytag>By Jared Kotler, Associated Press Writer</bytag>
1279</byline>
1280<dateline>
1281<location>Bogota, Colombia</location>
1282<story.date>Monday January 25 1999 7:28 ET</story.date>
1283</dateline>
1284</body.head>
1285</body>
1286</nitf>  
1287  
1288---  
1289  
1290
1291
1292* * *</tfoot></tbody></thead></xml></xml></table></gangster></gangster></person></person></a></the_title_of_the_book></book_title></last_name></first_name></body></from></to></body></from></to></letter></letter></p></p></from></to></h1></p>

XML Basic-from w3schools.com