XML standard was created to provide an easy-to-use and standardized way to store self-describing data (self-describing data is data that describes both its content and its structure).
XML, the Extensible Markup Language, is a W3C-endorsed standard for document markup. It defines a generic—syntax—used to markup data with simple, human-readable tags. It provides a standard format for computer documents that is flexible enough to be customized for domains as diverse as websites, electroni6 data interchange, vector graphics, genealogy, real estate listings, object serialization, remote procedure calls, voice mail systems, and more.
It is a subset of SGML (Standard Generalized Markup Language) the most visible definition for it is:
"Extensible Markup Language (XML) is a subset of SGML that is completely described in this document. It is the goal to enable generic SGML to be served, received, and processed on the web in the way that is now possible with HTML. XML has been designed for ease of implementation and for interoperability with both SGML and HTML".
XML is a markup language for documents, containing structured information. 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 some structure.
A markup language is a mechanism to identify structures in a document. The XML specification defines a standard way to add a markup to documents.
