Tracker's Identify Command

One of the first things that many people do upon installing the BeOS is start poking around everywhere they can, just to see what it all looks like, what features are there, etc. Since the Tracker is the first application most people use, it's natural to start exploring with it. And again, quite naturally, the first thing most people check out, after opening a few folders, is the menus in each Tracker window.

Not too far into their exploration, they come to the second to last item of the first menu, the Identify command in the File menu. They notice that the command is only enabled if there are some files selected, select some files, and choose the menu command.

And nothing happens.

At least, that's the experience many people had in the two different Preview Releases. In Release 3, the effects of the Identify command are more immediately noticed. But to understand what's happening, and what used to happen, you need to know a bit about MIME types.

Most desktop operating systems these days have some way to give files a "type," and to say what application should open the file. On Windows, it's the "dot extension," the three or four characters after a period at the end of a file name. On the Mac OS there is a hidden type and creator code. On the Internet, when sending files across the wire, say, when you download a movie or a compressed application, the download is preceded by the file's MIME type. MIME types are an industry standard way to designate the type of a file, and are the defacto standard for the Internet.

Because of the importance of the Internet, and of the richness of the MIME standard, the BeOS uses MIME types as the native method of identifying files. This way there is no (sometimes error-prone) translating between MIME and whatever mechanism the operating system has decided to use. The MIME type is stored as an attribute of the file (attributes are one of the more interesting features of the BeOS file system).

For a variety of reasons, files don't always come to the BeOS with BeOS file system attributes on them. Most files on the Internet are compressed into archives; the archive itself has a MIME type from the Internet transmission, but the files inside it may not -- few other operating systems use attributes on files as extensively as the BeOS.

Before the Tracker can show you a file's correct icon, before it can open the file, etc., the Tracker needs to figure out what kind of file a previously unidentified file is. The BeOS runs a periodic "sniffer" process that will identify files and add the correct file attribute to the file, but this happens when your system is idle. Sometimes you want the BeOS to do it right away so, as you've probably figured out by now, the Identify command is a way to force the Tracker to try to figure out the file's (or files') type immediately.

In the BeOS Preview Release 1 and 2, the Tracker's window needed to be closed and then re-opened before the Tracker would show the effects of the Identify command. Since Identify runs so quickly, there was no real indication that anything had happened, which confused people. With Release 3, however, the Tracker will re-draw the file's icon immediately upon Identifying it, so you get a better sense of what has happened.

Next week we'll talk even more about MIME, and maybe even whisper a bit about the dreaded MIME Police.