XML is designed to facilitate the open exchange of information. It defines a syntax that you can use to create your own markup language and provides access to complex data sets over multiple platforms. XML is used to create custom tags that best describe the contents of data rather than the format or presentation of data. An XML file is made up of elements, each of which consists of a start tag (<title>), an end tag (</title>), and the information, or content, between tags.
For example, an XML element might be tagged as <name>, a <enzyme>, or a <sequence>.
Separating data from presentation enables the seamless
integration of data from diverse sources.
Essentially, XML focuses on providing information about data and
how it relates to other data. HTML
on the other hand, is concerned with the format of data.
The following demonstrates the difference between HTML and XML:
Comparison of HTML and XML tagging
As the example below demonstrates, XML and HTML differ in how tags are used.
<h2 align="center"> My Second-Level Heading, Centere d</h2>
<ul>
<li type="square"> My first list item, with square bulle t</li>
<li type="square"> My second list item</li>
</ul>
The example above shows how HTML tags describe content and layout. <h2>,
<ul>, and <li> are elements, sometimes called tags. In the HTML tagging above,
align is an attribute of the <h2> tag. XML uses elements and attributes in a sim-
ilar way. Below is an example of XML tagging that demonstrates how XML uses
tagging differently to organize information.
<Metabolic_reaction>
<name>arginase catalysation</name>
<compartment>cytosol</compartment>
<reversibility>false</reversibility>
<reactant>
<name>L-arginine</name>
<stoichiometry>1</stoichiometry>
</reactant>
<product>
<name>L-ornithine</name>
<stoichiometry>1</stoichiometry>
</product>
<enzyme>
<name>arginase</name>
</enzyme>
<kinetics>
<function>M-M</function>
</kinetics>
</Metabolic_reaction>
Rather than describing the order and fashion in which the data should be displayed,
the XML tags indicate what each item of data means. This data can then
be decoded and used in specific and customizable ways.
Document Type Definition (DTD)
XML is able to generate elements that are tailor made by the
specific group using the language. This is achieved through Document Type
Definition. A DTD is essentially a tag-set definition that lists the
tags and attributes and tag-nesting conventions allowed.Each
implementation of XML is defined by a DTD. Therefore, it is the DTD that
provides the consistency of how information is presented and ultimately
shared. DTDs let you specify the kinds of tags that can be included in
the XML document, defining the rules of the document, such as which elements
are present and the structural relationship between the elements. An XML
parser reads in XML data from an input source and checks it against the
rules defined in the DTD to make sure the data is structured correctly.
XML Schema
XML Schema is information modeling language for XML
developed by W3C. It incorporates ideas from SOX and XDR, and can full support
for datatypes
- Built in types (integer, boolean, etc.)
- Custom types (telephone numbers, etc.)
The differences between DTD and XML Schema in data typing
and syntax:
