Explain about Basic XML.

XML–Extensible markup language, XML is a markup language to construct cross environment compatible data.

XML data is – operating system, hardware language & computer architecture independent.

These features makes XML data as cross environment compatible data. XML data is constructed through tags and attributes.

Difference between  XML  and HTML :

1.Both are Mark up languages  because they use tags.

2.HTML concentrates on the process to  present data and used to design   web  pages  of  websites .

3.In  HTML  all  tags  are predefined  tags.

4.XML  is used  to  construct  the data  and to  describe  the data .It  is not  suitable  for  designing  web Pages .

5.In  XML  all tags are uses defined  and  pre defined .

6.XML  is  complement  to HTML  but not  the replacement  of HTML.

7. XML   file’s  data  is formatted data.

8. Data in text  file’s   does not  show  relationship  between values  and no data hierarchy.

9. Data of the XML  files  show  relation ship  between values and follow data  hierarchy.

valid (or)  well  formed :

XML  documents may be either valid (or)  well formed . The XML  document that  satisfies  syntax  rules  and naming rules  is  called well  formed  XML  document .

XML engine (or) XML   parses is  required to check  whether  XML  document is  well formed (or)  not  XML  document  that   satisfies syntax  rules, naming, rule and  DTD/ schema  rules is  called‘ Valid  XML   document’.

Syntax rules:

Every  opening tag  should  have closing tag.

sub tag must be nested  properly.

You should not  keep any tag after   closing the loot element.

XML tag name  and attribute  name are case  sensitive .

Naming Rules :

Tag name must  start  with  alphabet.

Other  than first  character of tag  name can be alphabet, digit, - , underscore (-) but other special characters are not allowed.

HTML tag name and attribute name are case sensitive.

White space characters are not allowed.

XML Elements:-

XML document are composed of three things:

1) Elements

2) Control information

3) Entities.

Elements:-  Each document has a single root element which contain all of the other markup.

Nesting tag:- Event the simplest document has nested tags unlike HTML these must be nested properly and closed in the reverse of the order in which they are opened.

Case sensitive:- In HTML we use mixed upper case and lower case inside markup. XML is case sensitive and you must use lower case for markup.

In HTML  < img src = “c:\document\il.jpg” height = “120” Width = “30”>- - - - </img>

In XML this tag will be written as

<img>

<src> “C:\document\il.jpg” </src>

<height> 120 </height>

<width> 30 </width>

</img>

Control Information:- Control structures are

comment 

                         

document type

processing instruction  declaration

Comment:- <! – – comment text – – >

Processing instruction:- The instruction tells the application that the data in the file follow the rules of XML version 1.0.

< ? XML version = “1.0”? >

Entities:- The final part of the XML may be one (or) more entities. Entity is a thing which is to be used as a part of the document. Example of an entity is image (or) encrypted signature etc.,

Syntax: > – &gt;

              < – &lt;

Eg:- <msg> 10 >15 </msg> 

       < msg> 10 & gt; 15 </msg>