XML stands for Extensible
Markup Language, and is the defacto standard data interchange
language. The goal of XML is do for data interchange what HTML did for
XML defines a set of rules that all conformant XML documents must
follow. All XML documents must be well-formed.
All element tags in a well-formed XML document must either have
matching start tags and end tags (e.g. <element-name;>
... <element-name>), or follow the correct format for
an empty element (e.g. <element-name />).
Special characters such as <,
>, &, ' and
" must be properly escaped as an entity
reference in a well-formed document.
All elements must be properly contained in the parent element.
Constructs such as <element-a> ... <element-b>
... </element-a> ... </element-b> are not
allowed in a well-formed XML document.
These stricter rules on a well-formed XML document makes XML easier to
parse than HTML documents.
Furthermore, an XML document can be valid if
A set of rules defining the valid elements and attributes that
can be present in the document has been defined. There are
currently 2 ways of defining these rules, through
and Databases: Discussion of data vs document centric XML,
when to use native XML databases, how to map XML to relational
or object oriented databases and characteristics of native XML
databases to consider.
Applications and Uses of XML
XML has been applied and used in many different domains, in areas
as diverse as data store, ontologies, graphics and remote procedure
calls. Some examples are listed in this section.
SVG: a vector-based
graphics format defined for web applications
Web Services: emerging
industry standard for allow callable services to be made
available on the web, allowing the construction of distributed,
heterogeneous applications. Key components of web services
(service message format), WSDL (service
UDDI (service directory for discovery).
Open Document: an open document format for word processing,
spreadsheet and presentation documents exchange. Based on the
OpenOffice XML file
format, and adopted by products such as
Extensible User Interface Language. This is an XML based
language for defining cross-platform user interfaces.
Developed and used by mozilla.org in the Mozilla
suite of products, this has inspired similar efforts by Microsoft (in
XAML) and others.