A number attached to a specific version of a software item and used to distinguish this version from other versions. Simple version numbers are usually allocated in sequence so that successive version numbers will correspond to successive versions. Version numbers can also be composite, consisting of several parts often separated by periods. This numbering scheme allows a hierarchical identification of versions and is one way of distinguishing potential subsets among a set of versions. Configuration management approaches and configuration management tools must define a strategy for numbering versions.