HTML is an application of the Standard Generalized Markup Language (SGML) which is the International Standard (ISO 8879) for text markup. The principle is that text markup concentrates on structure rather than appearance, making the files more reuseable and leaving the visual details to the end-user software (like the browser you're reading this with now).
HTML is an application of ISO Standard 8879:1986 Information Processing Text and Office Systems; Standard Generalized Markup Language (SGML). The HTML Document Type Definition (DTD) is a formal definition of the HTML syntax in terms of SGML.
Standard Generalized Markup Language (SGML) is an international standard (ISO 8879) used for document representation and electronic interchange. It is being used by an ever-increasing number of organizations to facilitate the creation, management, storage and delivery of document-based information. As a standard, SGML goes far beyond the goal of information interchange; it is also a tool for managing and protecting an organizations data assets.
History of SGML
Why SGML was created
- While leading IBM research on integrated law office information systems in the 1960s, Charles Goldfarb and his team created a method ("Generalized Markup Language") to let text editing, formatting, and information subsystems share documents. Over the course of nearly two decades and through the efforts of many people and groups, GML eventually gave rise to SGML. In 1986, SGML was adopted as a standard of the International Organization for Standardization (ISO 8879). Since then, it has been increasingly adopted as the international standard for data and document interchange in open system environments, including the automotive, defense, commercial aerospace, pharmaceutical, electronics, and telecommunications industries.
- Standard Generalized Markup Language is a data encoding that allows the information in documents to be shared -- either by other document publishing systems or by applications for electronic delivery, configuration management, database management, inventory control, etc.
- Because it provides a vendor-neutral, formal, international standard for information interchange, SGML is being widely adopted for sharing document-based information in open systems environments.
Benefits of SGML and open systems
There are three key benefits of the open systems approach that employs SGML:
- Investment protection. By putting strategic documents into SGML, organizations protect their information investment from being locked into a single vendor's technology or methodology.
- Data re-usability. By tagging data with its role and any other useful identifiers, SGML allows information to be readily located and re-used.
- Interoperability of applications. SGML is the lingua franca of open systems document applications. This means that customers can choose "best of breed" tools to create, manage or retrieve documents and the data in documents.
are logical Components and are identified in documents using tags
define symbolic names, e.g., é = é
A document consists of: SGML Declaration, Document Type Definition (DTD), Document Instance
<! -- DTD for simple office memoranda --> <!ENTITY % doctype "memo" --document generic identifier --> <!-- ELEMENT MIN CONTENT (EXCEPTIONS) --> <!ELEMENT Memo - - ((To & From), Body, Close?) > <!ELEMENT To - O (#PCDATA) > <!ELEMENT From - O (#PCDATA) > <!ELEMENT Body - O (P*) > <!ELEMENT P - O (#PCDATA|Q|Pref*) > <!ELEMENT Q - - (#PCDATA) > <!ELEMENT Pref - O EMPTY > <!ELEMENT Close - O (#PCDATA) > <!-- ELEMENT NAME VALUE DEFAULT --> <!ATTLIST Memo STATUS (confiden|public) public > <!ATTLIST P id ID #IMPLIED > <!ATTLIST Pref refid IDREF #REQUIRED >