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Nomenclature

  • Parser. A specialised software application for navigating through structured data.
  • Markup. The process of identifying and encoding data entities within arbitrary data.
  • Prologue. A segment of initialising data or code, typically required as an element of processing.
  • Tag. In XML context it is an identifiably named paired structure (start tag and end tag) used to enclose the data.
  • Attribute. Contextual information pertaining to an element
  • Element. In XML context and element represents the tag and all other related entities such as the data constituent and elements.
  • Schema. A form of data definition for an XML document.
  • Encoding. Has several contextual meanings but typically refers to the character set encoding of a particular document.

The What, Why and Where of XML

What is XML (eXtensible Markup Language)?

XML (eXtensible Markup Language) is a digital standard for describing structured and partially structured data. The XML data model and other features are extensively described in the W3C published standards documents:

XML specification and standards documents

  1. XML Standards (Fifth Edition)
  2. XPath Specification
  3. XSL Transformations (XSLT)
  4. XQuery and XPath Data Models
  5. XML Schema Definition

XML was approved and published as a standard by the W3C (World Wide Web Consortium) in 1998. The standard itself is a derivative of "Standard Generalised Markup Language" (SGML). Thus it is quite similar in many characteristics to another SGML derivative, HTML.

SGML itself is a derivation of GML - "Generalized Markup Language" and BNF - "Backus-Naur Form".

Why is XML?

There are numerous reasons for using XML.

  1. Can be used to store arbitary data.
  2. Typically intended to be in a form that is human and machine readable.
  3. Simple structured open format for long-term sustainability.
  4. Mature, established and stable. BNF/GML was in use in the late 1950's.
  5. It can express data as a tree, mitigating the need for the complex interactions required for platforms such as relational databases.
  6. It's a free, open standard maintained by the W3C (World Wide Web Consortium).