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Versioning Schemes

The most common software versioning scheme is a scheme in which different major releases of the software each receive a unique numerical identifier. This is typically expressed as three numbers, separated by periods, such as version 2.4.13. One very commonly followed structure for these numbers is:

major.minor[.revision[.build]]

or

major.minor[.maintenance[.build]]

In most commercial software, the first released version of a software product has version 1.0. Numbers below 1 mean alpha or beta versions, i.e., versions for testing purposes or internal use, or versions that aren't stable enough for general or practical deployment.

In principle, in subsequent releases, the major number is increased when there are significant jumps in functionality, the minor number is incremented when only minor features or significant fixes have been added, and the revision number is incremented when minor bugs are fixed. A typical product might use the numbers 0.9 (for beta software), 0.9.1, 0.9.2, 0.9.3, 1.0, 1.0.1, 1.0.2, 1.1, 1.1.1, 2.0, 2.0.1, 2.0.2, 2.1, 2.1.1, 2.1.2, 2.2, etc. Developers may at times jump (for example) from version 5.0 to 5.5 to indicate that significant features have been added, but not enough to warrant incrementing the major version number.

A different approach is to use the major and minor numbers, along with an alphanumeric string denoting the release type, i.e. 'alpha', 'beta' or 'release candidate'. A release train using this approach might look like 0.5, 0.6, 0.7, 0.8, 0.9 == 1.0b1, 1.0b2 (with some fixes), 1.0b3 (with more fixes) == 1.0rc1 (which, if it's stable enough) == 1.0. If 1.0rc1 turns out to have bugs which must be fixed, it turns into 1.0rc2, and so on. The important characteristic of this approach is that the first version of a given level (beta, RC, production) must be identical to the last version of the release below it: you cannot make any changes at all from the last beta to the first RC, or from the last RC to production. If you do, you must roll out another release at that lower level.

This is to permit users (or potential adopters) to evaluate how much real-world testing a given build of code has actually undergone. If changes are made between, say, 1.3rc4 and the production release of 1.3, then that release, which asserts that it has had a production-grade level of testing in the real world, in fact contains changes which have not necessarily been tested in the real world at all. This approach commonly permits the third level of numbering ("change"), but does not apply this level of rigor to changes in that number: 1.3.1, 1.3.2, 1.3.3, 1.3.4... 1.4b1, etc.

phpBB Versioning Scheme

The versioning scheme used by phpBB is related to the Linux Kernel versioning scheme. That is, stable branches have a middle number which is even, and unstable or development branches have an odd middle number. Major versions less than one are also considered unstable. The third number is incremented for maintenance releases. The first number only changes when major code rewrites occur.