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XML Technologies

Learn about XML, a markup language designed for carrying and storing data. Understand the difference between XML and HTML, how XML allows for easy data sharing, and explore XML tree structures and commandments.

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XML Technologies

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  1. XML Technologies XML

  2. What is XML? • XML stands for EXtensibleMarkup Language • XML is a markup language much like HTML • XML was designed to carry data, not to display data • XML tags are not predefined. You must define your own tags • XML is designed to be self-descriptive • XML is a W3C Recommendation

  3. XML vrs HTML • XML • Is a meta language • Focus on transport and storage of data • Not a replacement to HTML! • HTML • Is a vocabulary of SGML • Focus on display (formatting)

  4. XML is just pure information • Was not designed to do anything ... • Just structure, store and transport information <stickynote> <to>Joseph</to> <from>Tom</from> <body>Puchase tickets!</body> </stickynote>

  5. Format • The format of a .xml document is plain text • Only XML aware applications can interpret it correctly • But it can be easily viewed/edited by anyone using a simple text editor Tip: Internet Explore can be used as a viewer and validator of XML (Eg1, Eg2)

  6. Let’s be creative ... • 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 • That is because the XML language has no predefined tags, it’s a meta language! • The tags used in HTML (and the structure of HTML) are predefined. HTML documents can only use tags defined in the HTML standard (like <p>, <h1>, etc.) • XML allows the author to define his own tags and his own document structure

  7. Definition XML is a software and hardware independent tool for carrying information Note: the specification of the language can be found http://www.w3.org/XML/

  8. Content Vs. Layout • To display dynamic data in your HTML document, it will take a lot of work to edit the HTML each time the data changes • With XML, data can be stored in separate XML files • User can concentrate on using HTML for layout and display, and be sure that changes in the underlying data will not require any changes to the HTML • With a few lines of JavaScript, one can read an external XML file and update the data content of the HTML.

  9. Simple data sharing • Most systems have data in incompatible formats • XML is stored in plain text, thus it is software/hardware independent • Much easier to share information

  10. XML is a meta language! • As such, you can create new languages ... • XHTML the latest version of HTML  • WSDL for describing available web services • WAP and WML as markup languages for handheld devices • RSS languages for news feeds • RDF and OWL for describing resources and ontology • SMIL for describing multimedia for the web 

  11. XML Tree (1) • All xml documents are in the form of a tree <root> <child> <subchild>.....</subchild> </child> </root>

  12. XML Tree (2)

  13. XML Tree (3) • Simple example ... <stickynote> <to>Joseph</to> <from>Tom</from> <body>Puchase tickets!</body> </stickynote>

  14. XML Tree (4) • Root element <stickynote> • Children elements <to> <from> <body>

  15. XML Tree (4)

  16. 34U exercise  • Create the tree for ... <bookstore> <book category="COOKING"> <title lang="en">Everyday Italian</title> <author>Giada De Laurentiis</author> <year>2005</year> <price>30.00</price> </book> <book category="CHILDREN"> <title lang="en">Harry Potter</title> <author>J K. Rowling</author> <year>2005</year> <price>29.99</price> </book> </bookstore>

  17. XML Commandments

  18. Commandment 1 For every opening Tag, there must be a closing Tag <p>This is a paragraph <p>This is a paragraph</p>

  19. Commandment 2 XML Tags are case sensitive <Message>This is incorrect</message> <message>This is correct</message>

  20. Commandment 3 XML Elements Must be Properly Nested <b><i>This text is bold and italic</b></i> <b><i>This text is bold and italic</i></b>

  21. Commandment 4 XML Documents must have a root element <root> <child> <subchild>.....</subchild> </child> </root>

  22. Commandment 5 XML attributes must be quoted <stickynote date=1/10/2008> <stickynote date=“12/11/2007”>

  23. Commandment 6 Some characters have special meaning in XML <message>Meet me at Tom’s place</message> <message>Meet me at Tom &apos; s place</message>

  24. Commandment 7 Comments in XML <!-- This is a comment -->

  25. Elements Vrs Attributes <book category="CHILDREN"> <title>Harry Potter</title> </book> • book is an element • which can contain • other elements (such as title) • Or text content (such as Harry Potter in title) • category is an attribute • Whose value is CHILDREN

  26. What’s in a name? • 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

  27. Best (Name) Practices • Make names descriptive. Names with an underscore separator are nice: <first_name>, <last_name>. • Names should be short and simple, like this: <book_title> not like this: <the_title_of_the_book_which_i_am_currently_reading>.  • Avoid "-" characters. If you name something "first-name," some software may think you want to subtract name from first. • Avoid "." characters. If you name something "first.name," some software may think that "name" is a property of the object "first." • Avoid ":" characters. Colons are reserved to be used for something called namespaces. • XML documents often have a corresponding database. 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, but watch out for problems if your software vendor doesn't support them.

  28. More into attributes ... • Generally used to provide additional information not part of the data • Use quotes and for a quote within a quote, use “&quot;” • Some limitations of attributes • attributes cannot contain multiple values • attributes cannot contain tree structures • attributes are not easily expandable in future • If in doubt use elements

  29. Spot the difference ... <note date="10/01/2008"> <to>Tove</to> <from>Jani</from> <heading>Reminder</heading> <body>Don't forget me this weekend!</body> </note> <note> <date>10/01/2008</date> <to>Tove</to> <from>Jani</from> <heading>Reminder</heading> <body>Don't forget me this weekend!</body> </note> <note> <date> <day>10</day> <month>01</month> <year>2008</year> </date> <to>Tove</to> <from>Jani</from> <heading>Reminder</heading> <body>Don't forget me this weekend!</body> </note>

  30. Well formed documents ... • 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 be quoted

  31. Valid documents ... • Is a "Well Formed" XML document, which also conforms to the rules of a Document Type Definition (DTD) <!DOCTYPE note SYSTEM "Note.dtd"> <note> … </note>

  32. Example DTD • A DTD is used to define the structure of an XML document but its not in XML! <!DOCTYPE note [ <!ELEMENT note (to,from,heading,body)> <!ELEMENT to (#PCDATA)> <!ELEMENT from (#PCDATA)> <!ELEMENT heading (#PCDATA)> <!ELEMENT body (#PCDATA)> ]>

  33. Example XSchema • An XSchema is an XML alternative to a DTD <xs:element name="note"> <xs:complexType> <xs:sequence> <xs:element name="to" type="xs:string"/> <xs:element name="from" type="xs:string"/> <xs:element name="heading" type="xs:string"/> <xs:element name="body" type="xs:string"/> </xs:sequence> </xs:complexType> </xs:element>

  34. Errors! • Errors in XML documents will stop your XML applications • XML software should be small, fast, and compatible • HTML browsers will display documents with errors (like missing end tags) • HTML browsers are big and incompatible because they have a lot of unnecessary code to deal with (and display) HTML errors

  35. XML Viewing • Just use a normal browser ... • simple.xml • cd_catalog.xml • plant_catalog.xml

  36. Better XML Viewing • Just use the Cascading Style Sheet (CSS) • Without CSS • With CSS

  37. The CSS CATALOG { background-color: #ffffff; width: 100%; } CD { display: block; margin-bottom: 30pt; margin-left: 0; } TITLE { color: #FF0000; font-size: 20pt; } ARTIST { color: #0000FF; font-size: 20pt; } COUNTRY,PRICE,YEAR,COMPANY { display: block; color: #000000; margin-left: 20pt; }

  38. Even better XML viewing • Use XSLT • XSLT is the recommended style sheet language of XML • XSLT (eXtensibleStylesheet Language Transformations) is far more sophisticated than CSS • One way to use XSLT is to transform XML into HTML before it is displayed

  39. XSL Example • The XML • The XSL • The result

  40. Exercise • Amazon just commissioned you to create an XML file for the following book as follows: • Title A.I. a modern approach • Author Russel and Norvig • Publisher Prentice Hall • Date of Publication 2000 • ISBN 1234567 • Dimensions 10 x 5 • Number of Pages 500 • Comments 2 in store 1, 3 in store 2 • Review Quite interesting! • Image http://www.amazon.com/AIBook

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