FoCAL

—categories : Theory … - Paper: http://www.cse.chalmers.se/~bernardy/AConcflictFreeVersionControlSystem.pdf - Toy implementation: http://www.cse.chalmers.se/~bernardy/focal_Code_Anders_Petter.tar.gz


`Jean-Phillipe Bernardy`_ has suggested that the following could go an a wiki:

A “patch theory” should be divided into two parts:

  1. An internal representation for data. This should be general enough to allow for universal merge operation. (I argue that this should have a free abelian group structure). Advantages are that the system never prevents you to “try” a merge, or a rollback, or cherrypicking, etc.
  2. A relation between internal representation and external representation (ie. the unix filesystem). “Ideally” this should be a bijection, but in practice this can not really be achieved. In particular the translation from internal to external may produce “conflict tags” in the output.

On top of that all the goodies that come with usual VC systems can be implemented, usually by annotation of the internal representation an queries on this.

Why proceed as such?

  • Allows for total user-level liberty, as in state-based approach, while preserving the cleanness of operation-based.
  • This is a neat separation of concerns. In fact, the internal representation can be seen as an extension of the space of versions. This is an extremely common technique in mathematics to improve orthogonality: eg. from naturals to integers to rationals, etc.