Operating systems also give us the ability to set up links to files (i.e., shortcuts in Windows, aliases on the Macintosh, and symbolic links in UNIX). QDL supports this functionality. So any folder, document, or section within a document in QDL might be the original, or it might be a link to the original, because we needed the information to show up in more than one place.
Linking is extremely useful. Copying and pasting information isn't a bad thing, until you find yourself having to do it over and over again, to keep the copies up-to-date when the source material changes. Linking allows us to dynamically draw the material from the source every time, eliminating the disconnect inherent in copying and pasting.
QDL extends the convenience and economy of linking down to the sub-section level within documents. Combined with QDL's ability to display nested information in place, linking takes on a whole new significance. Now we can quote other authors by linking to the sub-section of interest, instead of copying-and-pasting the text into our own documents.
So when do we copy-n-paste sub-sections from other documents? All the time! Especially in high-quality literature, we cite the original sources instead of making it all up as we go. This keeps the literature consolidated, and faciliates navigating the relationships among sources and derivatives. The problem with conventional document authoring systems is that developing and maintaining the source/derivative information is a completely manual process. We copy-n-paste the quote, and then manually add the source to a list of references. Later, somebody might manually enter the references into a database, to facilitate source/derivative searches. But in QDL, this all happens automatically. When we link a sub-section from another document into ours, we have already set up the relationship. QDL then allows us to navigate such relationships.
In some cases, we want to link to the latest and greatest version of the source material, such that improvements at the source will automatically improve our documents. In other cases, we want to link to the material as it was at a specific point in time. QDL also supports this. Then the linking simply eliminates the tedium and unreliability of manually maintaining the reference list, and makes it easy to navigate the source/derivative relationships.
In the broader sense, linking in QDL means that information can be organized topically, regardless of the source of the information. In other words, you can easily create folders that are collections of blog posts, bulletin board topics, private messages, wiki articles, and emails, all on the same topic. This is the way we organize the files on our hard-drives — not sorted out by the application that created them, but rather, by the topical nature of the material itself. QDL brings this concept to online information. And these aren't just link lists, where you assemble pointers to different types of information, and then click on them to send the browser to the web app that knows how to manage the data. The data can be opened in place, and viewed (or even edited) in the surrounding context.