url - Universität zu Lübeck

2.1. XML 9
being processed without any graphical aspects.
SGML was judged to be too complex to be used for web-based information processing
[100]: SGML contains many features that are very rarely used. Its support
for different character sets is weak which causes problems on the web where
people use many different platforms and programming languages. It is also difficult
to interpret a SGML document without having the definition of the markup
language (the DTD) available. These difficulties and the lack of SGML-related
software like editors have condemned SGML to being a niche technology rather
than a mainstream approach in document managing. Indeed some cynics have
renamed SGML to ’Sounds Good Maybe Later’.
To solve the complexity issue the eXtended Markup Language (XML) was designed
to be a simplified subset of SGML. It eliminates the features that make SGML
difficult to learn and parse while retaining most of the power of SGML. XML was
designed by the The World Wide Web Consortium (W3C) to be, in their own words,
”straightforwardly usable over the internet”. The W3C’s XML 1.0 recommendation
was first issued in 1998. The goals of XML as defined by the XML W3C Working
Group in the XML specifications [91] are:
• XML shall be straightforwardly usable over the internet.
• XML shall support a wide variety of applications.
• XML shall be compatible with SGML.
• It shall be easy to write programs which process XML documents.
• The number of optional features in XML is to be kept to the absolute minimum,
ideally zero.
• XML documents should be human-legible and reasonably clear.
• The XML design should be prepared quickly.
• The design of XML shall be formal and concise.
• XML documents shall be easy to create.
• Terseness in XML markup is of minimal importance.
2.1.2 Technical Introduction to XML
For space restrictions this thesis gives only a brief and informal introduction
to the eXtended Markup Language (XML). For more extensive information about
XML the reader is referred to popular online tutorials (e.g. [113]), books (e.g. [49])
and the W3C’s XML Specification [119].
For reasons of understandability XML is motivated and described with sample
documents - taken from the XMark project. XMark models an auction scenario
consisting of items, categories, sellers, and bidders. This way, a particular XMark