Have you ever pasted a graphic into a word processing document and later wanted to update it? It's a tedious process of opening the original file, making your changes, copying the new graphic, returning to the word processing document, deleting the old graphic, and pasting the new graphic. It doesn't have to be like this - applications can share data in a rich fashion that enables communication between the two applications. In fact, within limited spheres, some applications already do this, usually within a suite of programs from a single company. But a new open source technology, called LinkBack, promises to bring data linking to more Mac OS X programs. Such a technology would be welcome, since Apple has made various failed attempts at providing such connectivity over the years.
If you've been around the Macintosh world long enough, you might remember Apple's Publish & Subscribe technology. It appeared in System 7 back in 1991 and enabled you to "publish" data - a picture, some text, a chart - from one application and "subscribe" to it from another application - in essence, to insert a live copy of the published data into another document. That way, if you changed the graphic in the publishing application, the subscribed document would automatically receive the changes. Publish & Subscribe was a nice idea, but as late as 1994, I was commenting in TidBITS that it was a failure due to a poor implementation and minimal support from developers.
Then there was OpenDoc, a technology Apple introduced at the Worldwide Developer Conference in 1994 and which became real in late 1995 and early 1996. Apple never did a good job of explaining OpenDoc, but in essence it enabled a document-centric interface in which small modules - potentially from different companies - combined to provide the power of a monolithic application. The theory was great: you could put together exactly the word processor you wanted by adding together the best Find module, and the best Table module, and so on, and they would all fit seamlessly into the same interface. Despite the popularity of Apple's OpenDoc-based Cyberdog program (an integrated Internet client) and support from a few companies like Nisus Software, the reality never matched up to the theory, and Apple put OpenDoc and Cyberdog into "maintenance mode" in 1997. Interestingly, the OpenDoc community tried to negotiate a "stewardship agreement" for the OpenDoc Development Framework in exchange for Apple continuing to ship OpenDoc, but the deal fell through when the vice president who had agreed to this left Apple.
While Apple was working on the doomed Publish & Subscribe and OpenDoc, Microsoft developed OLE (Object Linking and Embedding), which remains in use within Microsoft applications today, and NeXT created Object Links in 1995.
LinkBack, an open source technology jointly announced by Nisus Software, The Omni Group, and Blacksmith, is a step in the direction of providing system-wide data linking again. With LinkBack, which will appear in future versions of Nisus Writer Express, OmniGraffle, OmniOutliner, Chartsmith, and Stone Create, if you want to edit a pasted graphic, you'll instead just double-click the graphic to edit it in the original application, after which your changes will automatically be reflected in the destination document. The pasted data doesn't have to be a graphic; it could also be text, such as stock quotes that you want to update automatically.
Of course, it remains to be seen just how well LinkBack works, and in particular, how well it avoids problems that have bedeviled all of these other data linking technologies in the past. Obviously, widespread support is tremendously important, since users won't even think about LinkBack unless it's widely available. The open source nature of the project should aid in adoption, especially since developers burned by Apple in the past won't worry that LinkBack will be at the mercy of a single company. It's also essential that LinkBack be reliable and easy to use, or the technology will have difficulty garnering an audience.
So if you're a developer, give LinkBack a look. Just because Apple's heavyweight data linking technologies have failed in the past doesn't mean the rest of us couldn't still use a good solution now.