What do the numbers in a version typically represent (i.e. v1.9.0.1)?
Maybe this is a silly question, but I've always assumed each number delineated by a period represented a single component of the software. If that's true, do they ever represent something different? I'd like to start assigning versions to the different builds of my software, but I'm not really sure how it should be structured. My software has five distinct components.
In version 1.9.0.1:
1: Major revision (new UI, lots of new features, conceptual change, etc.)
9: Minor revision (maybe a change to a search box, 1 feature added, collection of bug fixes)
0: Bug fix release
1: Build number (if used)—that's why you see the .NET framework using something like 2.0.4.2709
You won't find a lot of apps going down to four levels, 3 is usually sufficient.
There is the Semantic Versioning specification
This is the summary of version 2.0.0:
Given a version number MAJOR.MINOR.PATCH, increment the:
- MAJOR version when you make incompatible API changes,
- MINOR version when you add functionality in a backwards-compatible manner, and
- PATCH version when you make backwards-compatible bug fixes.
Additional labels for pre-release and build metadata are available as extensions to the MAJOR.MINOR.PATCH format.
It can be very arbitrary, and differs from product to product. For example, with the Ubuntu distribution, 8.04 refers to 2008.April
Typically the left most (major) numbers indicate a major release, and the further you go to the right, the smaller the change involved.
major.minor[.maintenance[.build]]
http://en.wikipedia.org/wiki/Software_versioning#Numeric
Numbers can be useful as described by other answers, but consider how they can also be rather meaningless... Sun, you know SUN, java: 1.2, 1.3, 1.4 1.5 or 5 then 6. In the good old Apple II version numbers Meant Something. Nowadays, people are giving up on version numbers and going with silly names like "Feisty fig" (or something like that) and "hardy heron" and "europa" and "ganymede". Of course this is far less useful because, you're going to run out of moons of jupiter before you stop changing the program, and since there's no obvious ordering you can't tell which is newer.