History Channel

SGML:Short History

In the late 1960s, as computers started to be used widely in certain arenas, a group called the Graphic Communications Association (GCA)created a layout language called GenCode. GenCode was designed to provide a standard language for specifying formatting information so that printed documents would look the same, regardless of the hardware's used.

In 1969, Charles Goldfarb led a group of people at IBM who built upon the GenCode idea and created what became known as the Generalized Markup Language (GML). Whereas GenCode was primarily a procedural or presentational markup language, GML aimed to define not only the appearance but to some degree the structure of the data.

Nearly 10 years after GML emerged, the American National Standards Institute (ANSI) established a working committee to build upon GML and create a broader standard. Coldfarb was asked to join this effort, and has since become known as the "father of SGML," which was the end product of ANSI efforts. The first draft of standard Generalized Markup Language (SGML)was made public in 1980; the final version of the standard emerged in 1986.

Since that time, the language has been enhanced as needed. For example, in 1988 a version of SGML was created that was designed specifically for military applications (MIL-M-(28001). SGML is called a metalanguage, Which is a language for creating other languages. sgml and xml is most important.

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Function of HTML

Function of Markup Languages

Markup languages are designed to instruct computers how to process data. The term markup derives from early print publishers, who would "mark up" text by hand to indicate to the printer which front size to use where, n which weight, using what form of alignment and so forth. In other words, the earliest markup languages were dedicated to passing formatting instructions.

Markup instructions are generally referred to as tags, and the process of marking up a document is sometimes called tagging. Early word-processing programs required the user to perform manual tagging. Today, most tagging is performed transparently in programs, and usually takes place using a proprietary system. The different methods for tagging text made it difficult for people to exchange data with each other. With the advent of Internet, it became more valuable and more imperative for authors to be able to interchange documents in a single format that was easy to use, yet powerful and aesthetically acceptable.

Markup specifically designed to affect the appearance of a document is commonly called presentation markup or procedural markup because it instructs the computer how to render the text. However, organizations that process huge numbers of documents, such as government and bureaucratic entities, quickly found that it was more important to know what the data represented rather than how it looked. Markup was then created to describe the content of the page. This type of markup is called logical or structural markup. Structural markup is also called descriptive or generic markup.

The following is HTML presentational or procedural markup for tagging the word "Summary" to appear in bold print:

            Summary                   

In logical or structural markup, it makes more sense to designate the word "Summary" as a section header, which describes not just its appearance but also its context in the document. The following is HTML structural markup for tagging the word "Summary" as a level-one heading:

             
 Summary 
              

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Learn HTTP Protocol

HTTP Tutorial

The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. This is the foundation for data communication for the World Wide Web (ie. internet) since 1990. HTTP is a generic and stateless protocol which can be used for other purposes as well using extension of its request methods, error codes and headers.

This tutorial is based on RFC-2616 specification, which defines the protocol referred to as HTTP/1.1. HTTP/1.1 is a revision of the original HTTP (HTTP/1.0) and a major difference between HTTP/1.0 and HTTP/1.1 is that HTTP/1.0 uses a new connection for each request/response exchange where as HTTP/1.1 connection may be used for one or more request/response exchanges.

Audience

This reference has been prepared for the computer science graduates and web developers to help them understand the basic to advanced concepts related to Hypertext Transfer Protocol (HTTP). After completing this tutorial you will find yourself at a moderate level of expertise in HTTP from where you can take yourself to next levels.

Basic Web Standards

Hyper Text Transfer Protocol(HTTP):

• GET request for information requests;
• POST request to provide additional information in a request; may have side effects;
• PUT request to upload information to server.

Hyper Text Markup Language

• Links generate GET requests for other pages;
• Image maps allow the selection of points or regions of images;
• Forms send attribute/value pairs to the server.