The Standard Generalized Markup Language is a standard for defining generalized markup languages for documents. ISO 8879 Annex A.1 states that generalized markup is "based on two postulates":
A fragment of the Oxford English Dictionary (1985), showing SGML markup
Database
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In computing, a database is an organized collection of data or a type of data store based on the use of a database management system, the software that interacts with end users, applications, and the
Standard Generalized Markup Language
…Rigorous: In order to allow markup to take advantage of the techniques available for processing, markup should rigorously define objects like programs and databases. DocBook SGML and LinuxDoc are examples which used SGML tools…
Collage of five types of database models