Introduction into the information-standard XML
XML is the abbreviation for “eXtensible Markup Language”.
In general, Markup languages help to identify structures (in documents), therefore markup langauges are a matter of great importance, because content almost always lacks of structure.
Moreover XML is not only a simple Markup Language as HTML, it is in fact a META-Markup Language, that allows you to define new markup languages based upon the standards defined by XML.
In order to begin to understand the higher levels of XML it is first important to hightlight the historical development of web languages and the reason why XML was developed.
At first there was the meta-language
Today we know the web-world as a network of blinking graphics, animation and many other multimedia-files and formats. The Internet’s founders never thought about the WWW as a getting that wide-ranging and unpredictable as it is today.
The web-based documents we understand as the today’s homepages are based on languages such as HTML which are again based on a more generic language, such at it was SGML and it is XML today.
Everyone knows about the problematic process of finding the right/desired information within the complexity of the document-jungle. One idea that possibly could support the search is to markup documents and other ressources insofar as to tell what your ressource/document/element is about or respectively what can be found within a certain area.
How does such a markup look like? – The following code-listing shows and example:
<header>On the Nature of Markup</header>
Markup languages were application-dependent in the beginning of the Sixties (60s). That also applied to the reading, wrting and editing of text within the different kinds of documents. Therefore IBM invented the idea of a meta-language and created GML. With the help of this meta-language it was possible to formulate and create a more specific (markup-)language for distributing, publishing and editing specific content/documents on any kind of application.
Its successor was the meta-language SGML (=the mother of all markup languages), which became an ISO Standard in the year 1986 and gave birth to a profile or respectively subset called XML, published as a W3C Recommendation in 1998. [Briggs02, Chapter 1]
The story continues in some days (translation of the german article not finished yet) …
Most important reasons why XML has evolved
- the need of separating content/data from presentation
- ease of using meta-languages (SGML was very complex and HTML inadequate)
- bridge transmission of data between different kinds of applications
- creating well balanced and well formed documents
- to make sense: necessary semantic information (deriving meaning from computer-understandable languages)
- XML Tutorial on w3schools
- More into XML; another article on this site: XLink and Xpointer
- XML Page on heise.de
- German Article on Selfhtml: Einführung / Web-Technologien / XML und XML-Derivate