Extensible Markup Language XML | Part 1

Extensible Markup Language XML | Part 1

Extensible Markup Language XML

XML (short for extensible Markup Language) is a markup meta language, or language syntactic marker that defines a mechanism that extends the meaning or control of other markup languages.

Is the attempt to produce a simplified version of SGML that allows for the designation simply new markup languages to use in web. The name thus indicates that it is a marker language (markup language) stretch (eXtensible) because it allows you to create custom tags.

The World Wide Web Consortium (W3C), after the browser war (i.e., the situation encountered in the nineties, such as Microsoft and Netscape introduced with each new version of its browser, proprietary extension to HTML Journal), was forced to follow the individual extensions to HTML.

The W3C had to choose which features to standardize and which to leave out of the official HTML specifications. It was in this context that began to emerge, the need for a markup language that would give greater freedom in the definition of tags, yet in a standard.

The “XML project, which began in the late eighties as part of the W3C SGML Activity, aroused such a strong interest to the point that the W3C created a working group, called the XML Working Group, composed of world experts SGML technologies, and a commission, XML Editorial Review Board, Member of the preparation of project specifications.

In February 1998, the specification became an official recommendation by the name of the Extensible Mark-up Language, Version 1.0. We soon realized that XML was not just limited to web context, but it was something more: a tool for use in various contexts, from the definition of the structure of documents, exchange of information between different systems, the representation image to the definition of data formats.

XML Uses

Compared to HTML, XML has a very different purpose: while the former defines a grammar for describing and formatting of web pages and, more generally, hyper texts, the second is a meta language used to create new languages, acts describing structured documents. While HTML has well-defined and restricted tags, with XML it is possible to define your own as needed.

XML is widely used today as a means for the export of data between different DBMS.

Technologies to XML

Schema languages (create new XML languages):

  • (DTD stands for Document Type Definition) is a document through which you specify the structural features of an XML document through a series of “grammatical rules”. In particular, it defines all the elements of XML documents, hierarchical relationships between the elements, the order of appearance in the XML document and which elements and which attributes are optional or not.
  • XML Schema: how the DTD is to define the structure of an XML document. Today, the W3C recommends that you put in the place of the DTD itself, being a new and advanced technique. Its symbol is XSD stands for XML Schema Definition.

Other technologies related to XML:

  • XLink: used to connect two XML documents in full, unlike the classic links that know HTML, XLink allows you to create multi-link and semantically advanced.
  • (XSL stands for eXtensible Stylesheet Language) is the language that describes the style sheet to an XML document. Its extended version is the XSLT (where T stands for Transformations).
  • XPath is a language with which you can identify portions of an XML document and is the basis for other tools for XML such as XQuery.
  • To support this primary purpose, it provides basic functionality for dealing with strings, numbers and Boolean data. Its operation is based on creating a tree from the syntax summary document and allows you to target a specific part through the nodes of the tree with the simple word path.
  • XPointer *: serves to uniquely identify specific portions of an XML document, then allows them access to other languages or interface objects.
  • XQuery query language is designed to be applicable to any kind of XML documents and relies on the use of XPath for specifying locations within documents. XQuery capabilities that allow it to draw from multiple data source to search, to filter the documents and bring together relevant content.
  • SAX (Simple API for XML) is a programming interface, implemented in several languages, that allows to read and edit XML documents. Through you can implement the SAX XML parser specific. SAX is event based, unlike DOM, and reacts to events by parsing the application report. It is for the programmer to implement methods to react to events parsing.
  • DOM: is a programming interface such as SAX, implemented in a multitude of programming languages for manipulating XML files. Sun built from an XML tree where each tree node corresponds to an element of the file, which is why this tree is based.
  • VTD XML [1] DOM is easy and quick to use than SAX and is therefore usually preferred by programmers to manipulate XML files, but the tree generated from DOM is maintained completely in RAM and hence is not You can use this interface to manipulate files that are larger than the available memory on your computer.
  • RSS is a standard that serves to create a document with a unique structure of the XML type, able to develop a simple data exchange between Web pages, accessible from any scripting language. Essentially it is an XML document the structure of the nodes and their tags have the same name.
  • SVG (Scalable Vector Graphics) and VML (Vector Markup language) are standard imaging vector that uses documents formatted in XML. It also serves to describe two-dimensional images, static and dynamic. Reading the instructions in the XML source document, the interpreter-based drawing figures until the image.
  • WDDX (Word Date Description Exchange) WDDX is a structure to hold data in the same structure of a database, created by Macromedia and Allaire and released at the Open WDDX Organization.