Interview Questions and Answers

• XML is the Extensible Markup Language. It improves the functionality of the Web by letting you identify your information in a more accurate, flexible, and adaptable way.
• It is extensible because it is not a fixed format like HTML (which is a single, predefined markup language). 
• Instead, XML is actually a metalanguage, a language for describing other languages which lets you design your own markup languages for limitless different types of documents. 
• XML can do this because it's written in SGML, the international standard metalanguage for text document markup (ISO 8879).

• A markup language is a set of words and symbols for describing the identity of pieces of a document (for example 'this is a paragraph', 'this is a heading', 'this is a list', 'this is the caption of this figure', etc). 
• Programs can use this with a stylesheet to create output for screen, print, audio, video, Braille, etc. 
• Some markup languages (eg those used in wordprocessors) only describe appearances ('this is italics', 'this is bold'), but this method can only be used for display, and is not normally re-usable for anything else.

Its goal is 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.

There are literally thousands of applications that can benefit from XML technologies. The point of this question is not to have the candidate rattle off a laundry list of projects that they have worked on, but, rather, to allow the candidate to explain the rationale for choosing XML by citing a few real world examples. 

• XML can be used to describe and identify information accurately and unambiguously, in a way that computers can be programmed to understand (well, at least manipulate as if they could understand).
• XML allows documents which are all the same type to be created consistently and without structural errors, because it provides a standardised way of describing, controlling, or allowing/disallowing particular types of document structure. [Note that this has absolutely nothing whatever to do with formatting, appearance, or the actual text content of your documents, only the structure of them.]
• XML provides a robust and durable format for information storage and transmission. Robust because it is based on a proven standard, and can thus be tested and verified; durable because it uses plain-text file formats which will outlast proprietary binary ones.