SGML (Standard Generalized Markup Language)
SGML is a standard for defining generalized markup languages for documents. Here are some key points about SGML:
History
- SGML was developed in the 1980s by Charles F. Goldfarb, Ed Mosher, and Ray Lorie at IBM.
- It was first published as an ISO standard (ISO 8879:1986) in 1986.
- The goal was to create a language that could describe the structure of documents independently of any software or processing tools.
Key Features
- Document Type Definition (DTD): SGML uses DTDs to define the rules for structuring documents. A DTD specifies what elements are allowed, where they can appear, and how they can nest.
- Generic Markup: Instead of predefined tags, SGML allows users to define their own markup tags, making it highly flexible for different document types.
- Extensibility: The ability to extend the markup language by defining new tags or changing the rules for existing tags.
- Separation of Presentation and Content: SGML promotes the separation of document structure from its presentation, which was revolutionary at the time.
- Platform Independence: SGML documents are designed to be portable across different systems and applications.
Applications and Influence
- SGML was influential in the development of later markup languages like HTML and XML.
- It was used in various industries for document management, particularly in publishing, where its ability to define complex document structures was beneficial.
- The complexity of SGML led to its evolution into simpler, more web-friendly formats, but its principles continue to underpin modern markup languages.
Challenges
- The complexity of SGML made it less popular for general web use, leading to the development of HTML which was simpler and tailored for web browsers.
- Parsing and processing SGML documents can be computationally intensive, requiring sophisticated parsers and validators.
Sources
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