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5.1. Background

5.1.1. History

Declarative content earned its name due to the style of programming that calls for specifying the desired result without specifying how to achieve it. Declarative programming was, and still is, a discipline. One of the early goals of declarative programming was the development of techniques that allow specifying layout of documents and constraints on this layout, using markup languages, without specifying the algorithms with which this layout is achieved. This background motivation instilled the name markup content.

Document layout software vendors were developing their own document structure, format and encoding, giving rise to interpretability issues. For example, proprietary markup languages have been used by word processors to address their need to describe how each part of the document was to look. Today, in the context of iTV and the Internet, declarative content and markup content refer to the same type of content. Standardization efforts were launched to address this problem. The first widely accepted declarative content language is the Standard Generalized Markup Language (SGML), defined in ISO 8879 [SGML]. SGML served as the foundation on which Hyper Text Markup Language (HTML) [HTML], eXtensible Markup Language (XML) [XML], and all other markup content formats were built. As of the writing of this text, some vendors, such as Adobe, still support SGML.


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