All about XML

XML

• Extensible Markup Language
• A computer language which uses mark up and is capable of being extended
• Mark up: (Literally) Notations or symbols that are used to correct in making up text and indicate how text should be displayed (<, >, ? etc..)
• Mark up refers to the sequence of characters or other symbols that can be inserted at certain places in text file, to indicate how a file should look when it is printed or displayed
• Extensible:  a program or programming language that is designed so that users and developers can expand or add to its capabilities.

Ex:

<name>vishwak</name>

<email>vishwak.kurapati@gmail.com  </email>

<number>9405881515</number>

Red- markups

Black- Normal text

Tags and elements:

<name>→start tag

</name>→end tag

/→slash or solidus

<name>vishwak</name>--> Element (element name must start with letter or underscore and can have letters, digits, period, underscore etc .. but not white space)

Element name is name

Element value is vihwak

Rules:

• XML element names are case sensitive
• XML document should have one root element
• Elements should not be overlapped

Structure of XML elements:

<parent>

    <child>

        <sub-child>…………..</sub-child>

    </child>

</parent>

XML declaration or prolog:

<? xml  version=”1.0” encoding=”UTF-8” ?>

version=”1.0” – Version of XML

UTF- Universal Character Set Transformation Format

There is no end tag for this, hence it is not an element it is a declaration.

• It is optional. If it is appears in document then it should be on top. Not even white space or comment come before it
• All XML parsers are required to support UTF-8 and UTF-16
• This declaration  is case sensitive

Attributes:

It specifies a single property for an element. It consists of name and value separated by equal sign.

<book name=”mine”>

name=”mine”→attribute

name →attribute name(case sensitive)

mine→value(Always within quotation marks , single or double)

• Attribute is only placed after the start tag with white space associated
• Only one value for the same attribute in the same start tag

References:

A reference is used to add additional text or markup in XML document, where an error may occur if the character is typed directly. Such as < , &, >, etc.. can be replaced by &amp;, &lt;, &gt;, etc.

• References start with & and ends with ;

References are of two types:

Entity references: starts with & and ends with ;

Character references: starts with &# and ends with ; ex: &#97→a, &#65→A, &#90→ z etc.

Comments:

Declaration: <!—comment goes here-->

→Comments are place anywhere expect inside tag and top of the XML

→XML comments cannot be nested

Empty XML elements: Elements with no value

<element></element>  or  <element/>

XML was not designed to display data like HTML. XML doesn’t have predefined tags.

Uses of XML:

XML can separate data from HTML.

XML is used to exchange data

XML can be used to share data

XML can be used to store data

XML can make your data more useful

XML can be used to create new *ML languages

Elements vs attributes:

Attributes cannot contains 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 Document Type Definition – DTD: Which is used to define legal elements of an xml document.