In software configuration management (SCM), delta refers to the difference between two successive versions. This term suggests that differences should be small (2% different in average). So, using it can vastly reduce the amount of memory required.

Delta can be defined in 2 ways,symmetric delta and directed delta.

A symmetric delta can be expressed as Δ(v1, v2) = (v1 \ v2) U (v2 \ v1), where v1 and v2 represent two successive versions.

A directed delta, also called a change, is a sequence of (elementary) change operations which, when applied to one version v1, yields another version v2. (note the coorespondence to transaction logs in datbases).