XML

Draft

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In principle, someone is working on it and there should be a better version in a not so distant future.
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Definition

• XML means "Extended markup language". XML is designed as a machine readable self describing text editable persistent store for data. XML is a formalism or a meta-language (not to be confounded with HTML, a language to describe the structure of Web pages)

XML concepts

An XML document can refer to a physical file, a database entry, a datastream (any appropriate "text" that is delimited).

Wellformedness

An XML document is well formed if and only if

There is an appropriate XML declaration at the beginning

• The document starts with an XML declaration that includes a version number (currently 1.0).

<?xml version="1.0"?>

This declaration can also contain encoding information. By default encoding isUTF-8):

<?xml version="1.0" encoding="ISO-8859-1"?>

XML documents are hierarchical

• begin-tags and end-tags that match
• No tags crossing like

  <i>...<b>...</i> .... </b> 

• There must be single root
  • It can only appear once and can not be used within other elements

Other features

• XML is case sensitive, "LI" is not "li" for example
• "Empty" tags must be self closing, e.g.

• Attribute values are quoted

<a href= " http://tecfa.unige.ch:8080/xml.html " >)

• Special caracters: <, &, >,", '
  • Use < & > &aquot; ' instead of <, &, >,", '
  • Including URLs !!

Valid

An XML document is said valid if it conforms to some kind of grammar also called schema.

The most popular ones are in this order:

• DTD
• XML Schema
• Relax NG

Text-centric vs. data-centric XML

Data-centric XML as opposed to the text-centric XML refers to XML whose primary audience is not a human reader, but a computer program which will process the information, respond to it, store data items in a database, and so on.

Software

(longer entries have their own page)

XML creation

• See XML editor

Validation

Off-line validation

• Most decent XML editors do offer validation functionality. However, some free XML editors do not. Some (like Xemacs) only offer limited verification.

• [xmllint]
• xmlTester.jar. This tools is based on the Xerxes parser.
• XML Nanny. XML Nanny is a Free Mac OS X developer tool that provides an Aqua interface for checking XHTML and XML documents for Well-Formedness and Validity either locally or across the network. (Tiger OS X 10.4) [sept 2005]

On-line validation

Note: You may need to change DTD's local system identifier. These programs must be able to get the DTD. I rather suggest installing a local program on your machine (like xmllint or xmlTester).

• STG XML Validation Form, curtosy of Scholarly Technology Group, Brown University
• XML well-formedness checker and validator, Richard Tobin, University of Endinburgh (RXP parser)
• XML.com's (simple well-formedness)

On-line validation for specific XML applications

• W3C HTML Validation Service This validator doesn't work with your own DTD's. Its primary function is to validate W3C vocabularies (HTML, XHTML, SVG, MathML, ... )

• FEED Validator. Validates various RSS Formats plus PIE

Links

Tutorials

• XML:Managing Data Exchange. Thi Wikibook project introduced XML from a Data exchange perspective.

News

• Cafe con Leche XML News and Resources (Best resource to keep in touch with XML-related news)

• TECFA's XML Page (DSchneider's "old" XML pointers page).

References

• Elliotte Rusty Harold, (2004). XML in a Nutshell, O'Reilly, Abstract/TOC ISBN 0-596-00764-7 (Best buy according to DSchneider).