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  • Technical Glossary

XML

What is XML?

XML is a tunable tag language for describing things in a hierarchical, formatted manner. For instance HTML, the language of all webpages, is a tuned version of XML.

XML is not particularly elegant, but it has become a standard. As a consequence:

  • there are many tools around for manipulating XML.
  • there may already by some tuned versions of XML for specifying items and contracts, which is what we want.
  • once GUIs will be developed none will have to see the underlying XML.

Basic Structure

  • Tags. The information in an XML file is stored inside tags. Tags are not predefined in XML: users must define their own ones.
  • Elements. An XML element is everything from (including) the element’s start tag to (including) the element’s end tag.
  • Attributes. An attribute is some extra information, provided at the start tag in quotation marks. They are intended to be metadata (data about data).

Here is an example of an .xml file:

<?xml version="1.0" encoding="ISO-8859-1"?>
<note id=“1245”>
  <to>Tove</to>  
  <from>Jani</from>  
  <heading>Reminder</heading>  
  
  <body>
    Don't forget me this weekend!
  </body>
</note>

In the example, note is an element and id is an attribute.

Defining XML structures

In XML, it is possible to define structures. Then, we can verify if a given xml file matches with this structure. For example, we can define a Contract and verify that a given file created by a user has a valid structure, according to the file that we have defined. We call this proccess Validation.

This definitions are made in external files. There are different documents to accomplish that:

  • DTD (Document Type Definition).
  • XSD (XML Schemas). Schemas are the most used way to the define a XML structure. The SXP Contract schema is an XSD.
  • Relax NG files.

XML Namespaces

In XML, it is possible to define namespaces in order to distinguish the authorship of the different tags.

Normalization organisms

There are many organisms that define protocols, schemas based on XML. Here there are some of the most importants:

  • W3C. International consortium that produces standards for the world wide web. They defined XML specification in the first place.
  • ISO. Organization that promotes worldwide proprietary, industrial, and commercial standards.
  • OASIS. Global consortium that drives the development, convergence, and adoption of e-business and web service standards.
  • IANA.

More content of XML

Here are the obvious pages about XML:

Generating PDFs from XML

See XML tools.