Sharing the Tight Way

Computerworld - I recently compared Microsoft's proposed solution to DLL hell with the way Unix developers avoid ".so" hell [Technology, Nov. 12]. The term .so stands for shared objects, which are more commonly known as shared libraries. They are basically the Unix equivalent of Dynamic Link Libraries (DLL).
Microsoft is proposing a complicated procedure that would require developers to embed version numbers within header files, as well as create many new registry entries in some cases and replace registry entries with XML files in others. The solution on Unix is to simply rename the library file.
Admittedly, my explanation of the Unix approach was a bit of an oversimplification. So allow me to elaborate by describing how shared libraries are handled on Linux, which is a Unix clone. Consider yourself warned, however, that what I'm about to describe isn't the official policy on how to manage .so versions in Unix or Linux. This is simply my observation of how Linux library maintainers generally work. There's probably an official policy guide on .so versioning, but more likely than not, it simply describes what Unix programmers already do, which is whatever makes sense at the time.
Imagine that a group of people maintains a fictitious library called "libwidgets." These folks are reasonably happy with their work and release Version 4.0 of this library. Version 4.0 gains widespread approval, and it becomes the de facto standard version for libwidgets.
So the next time you install a Linux distribution, it will probably install a file called "libwidgets.so.4." The distribution maintainers may also install one or more symbolic links to this file. (If you're not a Unix person, a symbolic link looks like a file but is only a pointer to a file. Think of it as something similar to a Windows "shortcut.") This is a brand-new version, so it's probably necessary to create only one symbolic link, such as libwidgets.so.4.0.
The only reason you may want this symbolic link is because someone may build an application that expects to load the file libwidgets.so.4.0 instead of libwidgets.so.4. If you try to run that application without first creating the symbolic link, the program will complain that it can't find the library it needs, because it will be looking for the wrong file name.
Naturally, libwidgets will change. People will fix bugs and add features. If the bug fixes are minor and don't seem to affect existing applications, it's up to the library maintainers, the Linux distributors or both to decide whether to change the version number of the