David Gelpi Fleta's List: XML

• • XML stands for EXtensible Markup 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
• The Extensible Markup Language (XML) became a W3C Recommendation 10. February  1998.
• XML was designed to transport and store data, with focus on what data is.
   HTML was designed to display data, with focus on how data looks.
• XML is not a replacement for HTML.
• XML was created to structure, store, and transport information.
• XML is Just Plain Text
• XML allows the author to define his own tags and his own document structure.
• • Recuerda citar en las actividades del grupo un ejemplo de uso de XML.
• XML will be used to describe the data, while HTML will be used to format and display the same data
• XML is a cross-platform, software and hardware independent tool for transmitting information.
• how quickly a large number of software vendors have adopted the standard.

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• With XML, data can be stored in separate XML files. This way you can concentrate on using HTML for layout and display,
• XML Simplifies Data Sharing
• databases contain data in  incompatible formats.
• XML data is stored in plain text format. This provides a software- and hardware-independent way of storing data.
• XML Simplifies Data Transport
• With XML, data can easily be exchanged between incompatible systems.
• Since XML data is stored in plain text format, XML provides a software- and hardware-independent way of sharing data.
• XML Simplifies Platform Changes
• Large amounts of data must be converted and incompatible data is  often lost.
• XML Makes Your Data More Available
• With XML, your data can be available to all kinds of "reading machines"
• XML is Used to Create New Internet 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 

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• <?xml version="1.0" encoding="ISO-8859-1"?>

• XML Documents Form a Tree Structure

    

  XML documents must contain a root element. This element is "the  parent" of all other elements.

    The elements in an XML document form a document tree.   The tree starts at the root and branches to the lowest level of the tree.

• All XML Elements Must Have a Closing Tag
• XML Tags are Case Sensitive
• XML Elements Must be Properly Nested
• <note date="12/11/2007">
• Entity References
• XML Documents Must Have a Root Element
• 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.
• (child elements
• &lt; < less than  &gt; > greater than  &amp; & ampersand   &apos; ' apostrophe  &quot; " quotation mark
• XML Attribute Values Must be Quoted
• With XML, White Space is Preserved
• Comments in XML
• <!-- This is a comment -->

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• What is an XML Element?

    

  An XML element is everything from (including) the element's start tag to (including) the element's end tag.

    

  An element can contain other elements, simple text or a mixture of both. Elements can also have attributes.
• XML documents can be extended to carry more information.
• XML Naming Rules
• no words are reserved.
• Best Naming Practices
• Make names descriptive
• Names should be short and simple
• Avoid "-"
• Avoid "."
• Avoid ":"
• use the naming rules of your database for the elements in the XML documents.
• Non-English letters

• 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
• make names descriptive.

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• XML elements can have attributes in the start tag, just like HTML.
• Attributes often provide information that is not a part of the data
• XML Attributes Must be Quoted
• either single or double quotes can be used
• <gangster name='George "Shotgun" Ziegler'>
• <gangster name="George 'Shotgun' Ziegler">

• Use of Elements vs. Attributes

   

  Data can be stored in child elements or in attributes.

• Avoid XML Attributes?  

    

  Some of the problems with using attributes are:  

    
   
  • attributes cannot contain multiple values (elements can)
   
  • attributes cannot contain tree structures (elements can)
   
  • attributes are not easily expandable (for future changes)
   
   

  Attributes are difficult to read and maintain. Use elements for data. Use attributes for information that is not relevant to the data.

• 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
   
   
• Try to use elements to describe data. Use attributes only to provide information that is not relevant to the data.

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• 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 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

• 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):

    

• Valid XML Documents

    

  A "Valid" XML document is a "Well Formed" XML document, which also conforms to the rules of a Document Type Definition (DTD):
• XML Schema is an XML based alternative to DTD.

• XML Schema  

   

  W3C supports an XML based alternative to DTD called XML Schema:

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• An XML data island is XML data embedded into an HTML page.

• <html> <body>

   

  <xml id="note" src="http://www.w3schools.com/note.xml"></xml>

• 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.

• Name Conflicts

   

  In XML, element names are defined by the developer. This often results in a  conflict when trying to mix XML documents from different XML applications.
• <h:table>
• <f:table>

• XML Namespaces - The xmlns Attribute

   

  When using prefixes in XML, a so-called namespace for the prefix must  be defined.

   

  The namespace is defined by the xmlns attribute in the start tag of an element.
• <h:table xmlns:h="http://www.w3.org/TR/html4/">
• xmlns:prefix="URI".
• <f:table xmlns:f="http://www.w3schools.com/furniture">
• xmlns:namespace-prefix="namespaceURI"
• Namespaces can be declared in the elements where they are used or in the XML  root element:
• 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.

• The namespace URI is not used by the parser to look up information.

   

  The purpose is to give the namespace a unique name

• 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.
• not so common type of URI is the Universal Resource Name (URN)

• Default Namespaces

   

  Defining a default namespace for an element saves us from using prefixes in all the child elements.
• <table xmlns="http://www.w3.org/TR/html4/">

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• PCDATA - Parsed Character Data

   

  XML parsers normally parse all the text in an XML document.
• CDATA - (Unparsed) Character Data

• 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.
• &lt; < less than  &gt; > greater than  &amp; & ampersand   &apos; ' apostrophe  &quot; " quotation mark
• 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.
• Nested CDATA  sections are not allowed.
• A CDATA section starts with "<![CDATA[" and ends with "]]>":

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• Parsing XML
• The parser reads XML into memory and converts it into an XML DOM object that  can be accessed with JavaScript.

• The XML DOM

   

   The XML DOM (XML Document Object Model) defines a  standard way for accessing and manipulating XML documents. 
• The DOM views XML documents as a tree-structure
• The elements, their  text, and their attributes are all known as nodes.

• The HTML DOM

   

   The HTML DOM (HTML Document Object Model) defines a  standard way for accessing and manipulating HTML documents. 

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• What is the DOM?

    

  The DOM is a W3C (World Wide Web Consortium) standard.

   

  The DOM defines a standard for accessing  documents like XML and HTML:

    

  "The W3C Document Object Model (DOM) is a platform and language-neutral  interface that allows programs and scripts to dynamically access and update the  content, structure, and style of a document."

• What is the XML DOM?

   

  The XML DOM is:

    
   
  • A standard object model for XML
   
  • A standard programming interface for XML
   
  • Platform- and language-independent
   
  • A W3C standard
• The XML DOM defines the objects and properties of all XML elements,  and the methods (interface) to access them.

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