XML(Extensible Markup language) and DTD(Document Type Defination) for XML in PHP

What is a XML?

• XML Stand fro Extensible Markup Language. 
• XML is a markup language much like HTML.
• XML was designed to store and transport data.
• XML was designed to be self descriptive.
• XML is a W3C Recommandation.It was designed to carry a data, not to display data.
• An XML document is plaintext and contains tags delimited by “<” and ”>”.
• Define a set of rules for encoading document in a format that is both Human-Readable and Machine-Readable.

We can use a XLM file into the PHP using simple_load_file(“ filename ”) function.

=> What is a DTD?

•  DTD Stand for Document type definition.
•  DTD is used to define the Structure of XML Document.
• Using DTD, XML file can carry a description of it’s own Format.
• Using DTD, you can verify that data receive from the outside World is Valid.
• DOCTYPE declaration is a Reference to an external DTD File.
• It is a also used to define special characters and Characters string used in the document.
• It define the structure with the list of legal elements.

  Example:- d1.dtd

             <! DOCTYPE note

             [

             <! ELEMENT note(to, from, heading, body)>

             <! ELEMENT to(#PCDATA)>

             <! ELEMENT from(#PCDATA)>

             <! ELEMENT heading(#PCDATA)>

             <! ELEMENT body(#PCDATA)>

              ]>

• !DOCTYPE note defines that the root element of a document is note.
• !ELEMENT note define that note element contain four element: “to, from, heading, body”.
• !ELEMENT to defines the element to be of type “#PCDATA”.
• !ELEMENT body defines the element to be of type “#PCDATA”.
• !ELEMENT heading defines the element to be of type “#PCDATA”.
• !ELEMENT from defines the element to be of type “#PCDATA”.

             How to use DTD file in XML?

              Example:- p1.xml