Introduction to XML History of XML Advantages of XML Syntax and structure of XML Rules of well...

Introduction to XML

History of XMLAdvantages of XML

Syntax and structure of XML

Rules of well formed XML document

Components of XMLXML Basics

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Content

• History of XML• Advantages of XML• Syntax and structure of XML• Rules of well formed XML document• Components of XML


History of XML

• Emerged as a way of its predecessors SGML and HTML

• Standard Generalised Markup Language is an extensible tool for semantic markup but pretty dam and complex

• HTML was free and simple but used only regular people


History of XML

• In 1996 there was a discussion about to find a extensiblity of SGML and simplicity of HTML

• W3C decide to sponsor a new markup language• Finally in 1998 W3C approved the Version 1.0 of

XML specification


What is 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


Difference between HTML and XML

XML HTMLXML 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 about carrying information

HTML is about displaying information


XML Naming Rules

• XML elements must follow these naming rules:

• Names can contain letters, numbers, and other characters

• Names cannot start with a number or punctuation character

• Names cannot start with the letters xml (or XML, or Xml, etc)

• Names cannot contain spaces • Any name can be used, no words are

reserved.


XML and Structured Data

• Pre-XML representation of data:

• XML representation of the same data:

“PO-1234”,”CUST001”,”X9876”,”5”,”14.98”

<PURCHASE_ORDER><PO_NUM> PO-1234 </PO_NUM><CUST_ID> CUST001 </CUST_ID><ITEM_NUM> X9876 </ITEM_NUM><QUANTITY> 5 </QUANTITY><PRICE> 14.98 </PRICE>

</PURCHASE_ORDER>


Advantages of XML

• The programmer are not restricted to use the limited set of tags

• With XML the programmer can create own tags• Each organization can build a library of tags• HTML consists of dozens of pre-defined tags but

XML is a tool used to generates markup language


Syntax and StructureComponents of an XML Document

<?xml version=“1.0” ?><?xml-stylesheet type="text/xsl"

href=“template.xsl"?><ROOT>

<ELEMENT1><SUBELEMENT1 /><SUBELEMENT2 /></ELEMENT1><ELEMENT2> </ELEMENT2><ELEMENT3 type=‘string’> </ELEMENT3><ELEMENT4 type=‘integer’ value=‘9.3’> </ELEMENT4>

</ROOT>

Prologue (processing instructions)

Elements

Elements with Attributes


Syntax and StructureRules For Well-Formed XML• There must be one, and only one, root element• Sub-elements must be properly nested

– A tag must end within the tag in which it was started

• Attributes are optional– Defined by an optional schema


• Attribute values must be enclosed in “” or ‘’• Processing instructions are optional• XML is case-sensitive

– <tag> and <TAG> are not the same type of element


Syntax and StructureWell-Formed XML?• No, CHILD2 and CHILD3 do not nest propertly

<xml? Version=“1.0” ?><PARENT>

<CHILD1>This is element 1</CHILD1><CHILD2><CHILD3>Number 3</CHILD2></CHILD3>

</PARENT>


Syntax and StructureWell-Formed XML?• No, there are two root elements


<CHILD1>This is element 1</CHILD1></PARENT><PARENT>

<CHILD1>This is another element 1</CHILD1></PARENT>


Syntax and StructureWell-Formed XML?• Yes


<CHILD1>This is element 1</CHILD1><CHILD2/><CHILD3></CHILD3>

</PARENT>


Components of XML

• XML declaration (or) Processing instructions• Elements and Sub elements• Elements with attributes


XML declarations

• Suggested by W3C specification• It is a processing instruction

• The processing instruction notifies the processing agent that the following document has been marked up as XML doc

<?xml version = "1.0"?>


XML declaration

• All XML declaration or processing instruction should begin with <? and ?>

• Following the <? You will find the name of processing instruction which in this case is “xml”


Attributes of XML declaration

• The XML processing instruction requires that you to specify a version attribute

• The others are optional attribute• Standalone• encoding


Attributes of the XML declaration

• VersionThe Version attribute allows

you to specify the current version of XML which is 1.0

• StandaloneThe standalone attribute specifies

whether the document has any markup declarations that are defined in a separate document


Attributes of the XML declaration

• EncodeAll XML parsers must support 8-bit

and 16-bit Unicode encoding


Elements

• Once declaring the processing instruction we need to start code the XML document

• Elements are the basic units of XML content• Every element consists of a start tag and an end tag

<NAME>Frank Lee</NAME>


• All XML documents must have at least one root element to be well formed.

• The root element, also often called the document tag,


Sample XML file<?xml version="1.0" encoding="UTF-8" standalone="yes"?><DOCUMENT><CONTACT><NAME>Gunther Birznieks</NAME><EMAIL>[email protected]</EMAIL><PHONE>662-9999</PHONE></CONTACT><CONTACT><NAME>Susan Czigany</NAME><EMAIL>[email protected]</EMAIL><PHONE>555-1234</PHONE></CONTACT></DOCUMENT>


XML’s hidden role in .NET

• XML use is ubiquitous throughout .NET• Web Services & XML

– Based on XML standards: SOAP, WSDL, UDDI, …

• XML in Configuration files– Application information stored in XML-based

configuration files


XML’s hidden role in .NET• XML&ADO.NET Data Access

– Provides conversion between DataSets and XML

– DataSets are serialized as XML


Web Services & XML

• Web Services are a very general model for building applications and can be implemented for any operation system that supports communication over the Internet.

• The web services are initially created with the help of a XML file


XML in Configuration files

• ASP.NET stores the settings in human readable format using the configuration files such as machine.config and web.config

• Here XML provides an all-purpose languages that is designed to let programmers to store data in customized and standardized way of using tags


XML&ADO.NET Data Access

• The internal format of the ADO.NET component use to store the data is actually in XML

• Normally with ADO components the data is exchanged in the binary format,which has difficulty in crossing the boundaries


XML &ADO.NET Data Access

• With ADO.NET components exchange pure XML which can flow over normal channels

• This XML format is extensible over to different operating system and non-Microsoft development language


NET XML Framework

• • Microsoft's.NET introduces a new suite of XML APIs

• – Built on industry standards• XML 1.0, Namespaces, DOM L2, XPath

1.0,• XSLT 1.0, XSD, SOAP, WSDL, UDDI• Commonly referred to as the .NET XML

stack


.NET XML Namespaces

• .NET XML stack is partitioned over several namespaces

• – System.Xml• – System.Xml.XPath• – System.Xml.Xsl• – System.Xml.Schema• – System.Xml.Serialization


Attributes

• Attributes are used to add extra information to an element

• Instead of using a sub tag we can use the an attribute

<?xml version=“1.0”?><Supermarket>

<Product id=“1” Name=“Chair”><Price=“45.60”>

</Product>


Using Attributes and Values

• Attributes in XML are more stringent• Attributes must always have values• Attribute values must be enclosed with

double quotes

Eg <Product name=“Chair”/> Acceptable

<Product name=chair/ Not Acceptable

<Product name /> Not Acceptable

Adding comments

• Comments are bracketed by the codes

<!– This is test file -->

<?xml version="1.0"?><Supermarket><Product ID="1" Name="Chair><Price ="45.67"></Product></Supermarket>


XML Syntax rule -I

• All XML Elements must Have a Closing Tag

<p>This is a paragraph</p> <p>This is another paragraph</p>


XML Syntax rule-II

• XML Tags are Case Sensitive• With XML, the tag <Letter> is different

from the tag <letter>.

<Message>This is incorrect</message> <message>This is correct</message>


XML Syntax rule-III

• XML Elements Must be Properly Nested

• Properly nested" simply means that since the <i> element is opened inside the <b> element, it must be closed inside the <b> element.

<b><i>This text is bold and italic</i></b>


XML Syntax rule-IV

• XML Documents Must Have a Root Element

• XML documents must contain one element that is the parent of all other elements. This element is called the root element.

<root> <child> <subchild>....</subchild> </child> </root>


XML Syntax rule-V

• XML Attribute Values Must be Quoted• In XML the attribute value must always be

quoted. Study the two XML documents below. The first one is incorrect, the second is correct:

<note date=12/11/2007><to>Tove</to> <from>Jani</from> </note>

<note date= “12/11/2007”><to>Tove</to> <from>Jani</from> </note>


XML Tree


XML Syntax rule-VI

• Entity References• Some characters have a special meaning in

XML.• 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.

<message>if salary < 1000 then</message>


XML Syntax rule-VII

• To avoid this error, replace the "<" character with an entity reference

• Replace the “<“ character with an entity reference



XML Syntax rule-VIII

• There are 5 predefined entity references in XML:

< < less than

> > greater than & & Ampersand' ‘ apostrophe " “ Quotation mark


Entities



XML Syntax rule-IX

• Comments in XML• The syntax for writing comments in XML is

similar to that of HTML.•


XML Syntax rules-X• With XML, White Space is Preserved• HTML reduces multiple white space characters to

a single white space

• With XML, the white space in your document is not truncated.

HTML: Hello my name is Tove

Output: Hello my name is Tove.


XML Namespaces - The xmlns Attribute

• The namespace is defined by the xmlns attribute in the start tag of an element

• The namespace declaration has the following syntax. xmlns:prefix="URI".

<h:table xmlns:h="http://www.w3.org/TR/html4/">


• In the example above, the xmlns attribute in the <table> tag give the h: and prefixes a qualified namespace.

• companies use the namespace as a pointer to a web page containing namespace information.

<root><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>


Uniform Resource Identifier

• 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


Syntax and Structure Namespaces: Overview• Part of XML’s extensibility• Allow authors to differentiate between tags of the

same name (using a prefix)– Frees author to focus on the data and decide

how to best describe it– Allows multiple XML documents from multiple

authors to be merged


• Identified by a URI (Uniform Resource Identifier)– When a URL is used, it does NOT have to

represent a live server


Syntax and Structure Namespaces: Declaration

xmlns: bk = “http://www.example.com/bookinfo/”

xmlns: bk = “urn:mybookstuff.org:bookinfo”

Namespace declaration examples:

Namespace declaration Prefix URI (URL)

xmlns: bk = “http://www.example.com/bookinfo/”


Syntax and Structure Namespaces: Default Namespace

• An XML namespace declared without a prefix becomes the default namespace for all sub-elements

• All elements without a prefix will belong to the default namespace:

<BOOK xmlns=“http://www.bookstuff.org/bookinfo”> <TITLE>All About XML</TITLE> <AUTHOR>Joe Developer</AUTHOR>


Default Namespace

• 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/"> <tr> <td>Apples</td> <td>Bananas</td> </tr> </table>

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