eXtensible markup language (XML) is a flexible and easy to use form of Mark Up meta language that can be used across the WWW and contains elements within open and close tags, and attributes which give properties or values to tags. It supports clear interfacing of information between many different types of programs and in many different user domains.
Despite the user flexibility in XML it has rules and XML code must be well formed and valid. One example of the structuring inherent in XML is shown in the Document Type Definition (DTD).
This example Document Type Definition (DTD) shows how a host system transferring address date to a delivery service handheld could constrain data to allow unambiguous transfer:
An example domain for the use of XML approach is Geographic information interchange which can be facilitated by a version of XML called GML (Geography Markup Language) and also GPX which has been created for exchange of GPS (global positioning satellite) information such as heading, track etc.).
The following extract from the Bos, B. (2001), “XML in 10 points” website describes the key attributes of XML and it’s user definable flexibility:
“Like HTML, XML makes use of tags (words bracketed by '<' and '>') and attributes (of the form name="value"). While HTML specifies what each tag and attribute means, and often how the text between them will look in a browser, XML uses the tags only to delimit pieces of data, and leaves the interpretation of the data completely to the application that reads it. In other words, if you see "
A key benefit of XML is that it separates document content from semantic or presentational information. This allows the transmission of information to different types of platform (PC, handheld, text reader) with decisions about presentation left until the delivery environment is known aiding interoperability across different types of web program.
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