In my Thinking XML column, I frequently focus on how various industries are working toward semantic transparency, which is the shared meaning of at least the framework of what is communicated in an XML document. Either the industries do so by creating complete document formats along with the semantics of all the elements, attributes, and content, or they define terms and concepts discretely and individually, independently of the documents in which they would appear. I call these approaches top-down and bottom-up, respectively, and very active communities provide useful material on each.
Because other articles in this issue of the Web Journal describe the motivations for XML and some of its goals, this article is intended to serve as a slightly more technical introduction to XML and as an overview of the specification. Throughout this document you will find references of the form [Section 1]; these are references to the XML language specification included in this issue. If you are interested in more technical detail about a particular topic, please consult the specification.
Operating systems -- and in particular their GUIs -- maintain structured, persistent data through a variety of mechanisms and in a variety of formats. Windows versions used INI files, then moved to a binary (and unified) registry; eariler versions of Mac OS had resource forks in the file system and a desktop file for its Finder; Linux and other UNIX-like systems typically used dotted, hidden files in home directories, with configuration detailed in dozens of incompatible ways between window managers and applications.
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