This concise but illuminating description of Standard Generalized Markup Language is not intended as a tutorial on using SGML. The authors discuss some of the historical background of SGML. They briefly describe its main competition, Open Document Architecture (ODA). They discuss the relationship between SGML and the markup language used on the World Wide Web, HTML. The descriptive approach used by SGML is contrasted with the procedural approach.

All in all, I found more insightful information in this brief paper than I have found in some books.