The Wikicalc puzzlers I got a chance to speak to Dan Bricklin last week about his forthcoming Wikicalc product, a spreadsheet in a wiki metaphor. It's easy to take for granted that these kinds of programs are easy to write but Dan described some of the inherent limitations of wikis that make Wikicalc such a challenge.

For example, wikis are not designed to support recalculation of a large spreadsheet. They're basically vehicles for displaying information. A wiki also doesn't understand the concept of interdependency, which is essential to a spreadsheet. You can change one cell in Excel and kick off 100,000 calculations. A wiki just doesn't know how to account for that. It's very good at noting that a word was changed or a sentence deleted but not that a formula in cell A189 changed a result in cell AB258.

Interdependence has other effects. I may be working on one page of my spreadsheet and you on another page. In a text world, that's reasonably easy to track. But if a formula on my page references a cell in your page, any changes you make will be overwritten by a change that I make. A wiki can deal well with pages, but not with pages that are linked to each other.

Also, people tend to work on spreadsheet models for a long time, trying out different what-if scenarios before saving. I could have my spreadsheet open for an hour working on a model that's changed in the meantime because someone else is working on the same spreadsheet. Then I save my file and overwrite the updates that were made by the other user. In essence, I write the old data back to the workspace because there was no way to lock the document while I was working on it.

Of course, Dan has figured out solutions to all these problems :-). Wikicalc will have a check-in/check-out function to limit versioning problems. He's also writing a sort of replication function that lets people work on a model offline and then upload the result while recording any changes. I'm not sure quite how he's doing that, but I'm sure it will be elegant.

There are a lot of exciting possibilities about this product. Imagine cells that refer to real-time temperature data or stock quotes on other websites and incorporate that data into calculations. You can do that with Excel, of course, but it's real hard to share.  ¶ 7:18 AM