Version Control Systems Version Control Systems Rahul Gopinath A moment from the history of linux kernel 

Version Control Systems are the lifeblood of Software Engineering. History Reproducibility Synchronization Concurrency Why? 

Concepts (C) Timeline (H) Choice Calculus (V) Representation (R) Structure of the talk 1 

C1 Versions Merges Tags Common Concepts 

Versions A box A large box A large blue box A small blue box C2 Revisions 

Versions A cup of water B A C A cup of milk A cup of cows milk A cup of coffee A cup of sea water C3 A cup of salty sea water A cup of hot coffee A cup of hot tea A cup of cold coffee Branches 

Merging water A small cup of water A cup of cold water A cup of water A small bottle of water A cup of cold sea water A small bottle of cold sea water C4 A small cup of water A cup of water A small bottle of water A small bottle of water C4 Revisions Branches 

Conflicts C5 water A small cup of water A cup of cold water A cup of water A small bottle of hot water A cup of cold sea water A small bottle of (hotcold) sea water 

Tags Alpha Beta Stable Demo C6 Next: Time line 

Early History Patchy Clear/Caster Source Code Control System Revision Control System Mainframe Dumb terminals H1 

Delta Storage Interleaved Composable (Forward| Reverse) H2 

Operation Based State Based A B C D E A B D E C History Models H3 

Client Server Generations Local Open Syntax Aware Architecture H4 R e p l i c a t e d 

Client Server Concurrent Versioning System Subversion Server Clients H5 

Replicated Clear Case Code Co-Op Past Watch Peers H6 

Open TeamWare Bitkeeper Git Mercurial Darcs Peers H7 

Syntax Aware Monticello MolhadoRef H8 Next: CC 

Choice Calculus : Syntax V1 Formal system to describe variations Dimension Choice Dim Platform in Platform is a web browser. Platform is an office suite. Tag Plain Text : Comon parts 

V2 Choice Calculus : Semantics dim Platform in dim UI in Platform is a web browser. Platform> is an office suite. Tag Selection {Platform.Linux,UI.KDE} → Firefoxi is a web browser. KOffice is an office suite Semantics {Platform.Win, UI.Gnome} => ie is a web browser. Office is an office suite {Platform.Win, UI.KDE} => ie is a web browser. Office is an office suite {Platform.Linux, UI.Gnome} => Firefox is a web browser. OpenOffice is an office suite {Platform.Linux, UI.KDE} => Firefox is a web browser. KOffice is an office suite 

V3 Choice Calculus : Alternate representations for choices dim Platform in dim UI in Platform is a web browser. Platform> is an office suite. Semantics {Platform.Win, UI.Gnome} => ie is a web browser. MSOffice is an office suite {Platform.Win, UI.KDE} => ie is a web browser. MSOffice is an office suite {Platform.Linux, UI.Gnome} => Firefox is a web browser. OpenOffice is an office suite {Platform.Linux, UI.KDE} => Firefox is a web browser. KOffice is an office suite dim Platform in dim UI in Platform is a web browser. UI,Platform> is an office suite. Equivalent to 

V4 Choice Calculus : Eliminate Redundancy dim Platform in dim UI in Platform is a web browser. Platform> is an office suite. Semantics {Platform.Win, UI.Gnome} => ie is a web browser. MSOffice is an office suite {Platform.Win, UI.KDE} => ie is a web browser. MSOffice is an office suite {Platform.Linux, UI.Gnome} => Firefox is a web browser. OpenOffice is an office suite {Platform.Linux, UI.KDE} => Firefox is a web browser. KOffice is an office suite dim Platform in dim UI in Platform . Platform> is an office suite. . Equivalent to 

V5 Choice Calculus : Embedded Dimension dim Platform in Platform is a web browser. Platform in UI> is an office suite. Tag Selection {Platform.Win} → ie is a web browser. MSOffice is an office suite Semantics {Platform.Win} => ie is a web browser. Office is an office suite {Platform.Linux, UI.Gnome} => Firefox is a web browser. OpenOffice is an office suite {Platform.Linux, UI.KDE} => Firefox is a web browser. KOffice is an office suite Next: Rep 

Modeling a Repository with Choice Calculus Modeling a Repository with Choice Calculus Temporal Ordering Dependencies C1 C2 C3 C1 C2 Branching Stable Release Dev Merges and Conflicts R1 

Choices Choices Change Set based | Snapshot based Revisions as: Tags | Dimensions Dim Rev in Rev Dim V.1 in Dim V.2 in V.2,f.2> Branches as: Top level Dims | Dependent Dims Dim Var in Dim V.1 in V.1> Dim V.1 in V.1 in Var> R2 

Dim Var in Dim V1 in Dim V2 in Dim V2’ in Dim V3 in Dim V3’ in Var,f.2>,f.3>,V3’,f.2’>,f.3’>> v.1 v.2 v.2’ v.3 v.3’ v.4 v.4’ Dim Var in Dim V1 in Dim V2 in Dim V2’ in Dim V3 in Dim V3’ in Dim V4in Var,f.2>,f.3>,f.1>,f.2’>,f.3’>,f.4>,V.3’,f.2’>,f.3’>> Dim Var in Dim V1 in Dim V2 in Dim V2’ in Dim V3 in Dim V3’ in Dim V4 in Dim V4' in Var,f.2>,f.3>,f.1>,f.2’>,f.3’>,f.4>,V.4’,f.2’>,f.3’>,f.4’>> R3 Before v4 After v4 After v4' Merges Merges 

Structure Structure V ::= D { V } | V; V | q=> V | 1 q ::= D.t Dim A in A<1,2> :: A Dim A Dim Bin A<1,2> :: A;B Dim A in A< Dim B in 1,2> :: A;A.a1 => B R4 Dim Var in Dim V1 in Dim V2 in Dim V2’ in Dim V3 in Dim V3’ in Dim V4 in Dim V4' in Var,f.2>,f.3>,f.1>,f.2’>,f.3’>,f.4>,V4’,f.2’>,f.3’>,f.4’>> :: Var,V1V2V2'V3V3'V4V4' 

Related Fields Concurrency: Software Transactional Memory Distributed and Versioned Data Bases Software Configuration Management 

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