A single entity contains source lines, being operated on by one or more end users. Within the same entity are entity version and level control data. Individual source lines contain version-related identification variables. After each version or level update by a user, a comparison is made between new and old versions; source line identification variables are modified, and new source lines are added; dependent version information is stored in the entity, and control data is updated. Subsequent retrievals of a version are responsive to the dependent version information, and produce indications of any changes that had been made to dependent versions.