"Document depository" means the document is in a format that can be automatically translated into other useful formats. For example, consider a document (under development) which may, in the future, need to be published as a report, a journal paper, a newspaper article, a webpage, perhaps a book, I (the author) am still uncertain. Formatting the document using "hard codes" (fonts, font sizes, page breaks, line centering, etc.) is rather a waste of time--styles vary very much between the particular document types and are publisher-dependent. The solution is to format the document using "logical" layout elements which may include the document title, chapter titles, subchapters, emphasis style, picture filenames, caption text, tables, etc. Thats what "docbook" does--it is a description of styles (using xml, a superset of html, and a close relative of sgml)--a so-called stylesheet. The logical layout is rendered to a physical appearance when the document is being published.
This section will be expanded in the future as we learn to use docbook.
