What is XML?
XML is a markup language for documents containing structured informations. Structured information contains both content(words, pictures, etc.) and some indication of what role that content plays(for example, content in a section heading has a different meaning from content in a footnote, which means something different than content in a figure caption or content in a database table, etc.). Almost all documents have same structure.
A markup language is a mechanism to identify structures in a document. The XML specification defines a standard way to add markup to documents.
Unlike HTML, XML tags identify the data, rather than specifying how to display it.
Where an HTMl tag says something like “disply this data in bold font”(<b>..</b>), an XML tag acts like a field name in your program. It puts a label on a piece of data that identifies it (for example: <message>…</message>).