4 Chapter 1. Introduction · Origin and Goals · Terminology This chapter lists the design goals that were laid out before the spec's development and clarifies potentially confusing terminology used in the spec's language. Extensible Markup Language, abbreviated XML, describes a class of data objects called XML documents and partially describes the behavior of computer programs which process them. XML is an application profile or restricted form of SGML, the Standard Generalized Markup Language [ISO 8879]. By construction, XML docu- ments are conforming SGML documents. Since the nineteen-eighties, object-oriented approaches to software engineering have contributed much to data modeling and system development. New tools and design techniques have provided ways to represent both real-world objects and abstract concepts as software objects instead of as