Adam Engst interviews Bruce Horn, who’s been working on a smart Finder-like browser called iFile:
iFile tracks any changes to the contents of the folders and automatically updates the database as required. For example, the user can drag in the Pictures folder and be able to browse all the images, create collections, etc., without actually copying any files or moving any data. iFile respects your directory structures and never modifies anything directly, in contrast to iPhoto, which copies images into its own directory hierarchy.
He also talks a bit about his contributions to the original Mac OS and how they translated to Mac OS X.
It turns out that Mac OS X still needed a creator mechanism by which individual documents could be opened by specific applications, so this information is stored in the resource fork of the file (of all places, since Apple is discouraging use of the resource fork), rather than simply in a creator code.
I had always thought that Launch Services stored these preferences in the ~/Library/ tree, but it turns out that choosing an application to open a file adds ‘icns’ and ‘usro’ resources to the file (and leaves the creator code intact). How odd. Changing the application back to the one whose creator code tags the file does not delete these resources.