SGML and XML
What is it all about?
SGML
SGML is an abbreviation of Standard Generalized Markup Language, a system for organizing and tagging elements of a document.
SGML was developed and standardized by the International Organization for Standards (ISO) in 1986.SGML itself does not specify any particular formatting; rather, it specifies the rules for tagging elements. These tags can then be interpreted to format elements in different ways.
SGML is used widely to manage large documents that are subject to frequent revisions and need to be printed in different formats.
XML
The Extensible Markup Language (XML) is a markup language whose specification was completed by the World Wide Web Consortium (W3C) in 1998.
The intent of XML was to define a markup language that facilitates development of documents that encapsulate descriptions of the information they contain. Introductory descriptions of XML generally contrast the language with the Hypertext Markup Language (HTML) - the predominant markup language in use today for display of information on the World Wide Web (WWW). HTML and XML are related in that they both provide specifications for marking up data in text-based documents, and both utilize tags adhering to a well-defined syntax for said markup.
However, this is where the similarity between the two ends. Specifically, HTML tags only facilitate describing how a particular collection of data in a given document should be displayed (e.g., bold face, underlined, in a particular font, tabulated, etc.). In contrast, the XML specification facilitates encapsulation of semantic meaning to the data contained within an XML document.
Moreover, while HTML provides a fixed set of tags for document markup, XML allows the document designer to specify any collection of tags required to associate a meaning with the data the document contains. In other words, XML can be considered a meta-markup language providing a standard against which an organization can define their own markup language.
Benefits of XML
An XML-centric approach to the development of a standard for data display information is desirable for several reasons:
1 - XML is easy to learn and allows one to represent data and the information it contains in a human-readable format.
2 - XML is an open or vendor-neutral standard. No single company maintains proprietary control over the standard. This is important when considering introduction of standards and proposals based on XML because it allows companies that have interests in use of the proposed standard to provide feedback on its development. Moreover, companies are more likely to incorporate use of the defined standard in their products because they understand that the open nature of XML ensures that they will have full access to the standard as it evolves.
3 - XML has already gained massive industry support from corporations such as Sun Microsystems, Microsoft, Oracle Corporation and numerous others. This suggests that any new standard based on XML will not quickly become dated or unsupported.
4 - A rich set of XML development and manipulation tools already exists. Development tools such as Sun Microsystem's JAXP API allow designers and developers to extend existing, proven technologies for manipulation of XML-based documents. The vendor-neutrality of XML allows the designer and developer to choose among several existing XML parsers. These aspects of the standard reduce the risk inherent in new software development efforts by providing tested and verified tools for common document processing requirements; thereby, freeing resources to concentrate their efforts on the processing requirements unique to the information their standard defines.
5 - XML is self-describing.That is, an XML document can incorporate all the information an application requires to interpret and process the document. This facilitates development of reusable software components that can be incorporated into various vendor applications that provide functionality for processing and manipulation of information defined by the XML-based standard.