1. 4 Version control (part 1)
Objektorienterade applikationer d2, förel. 4
4 Version control (part 1)
(Hodson: 1, Chacon: 1-2)
DAT055, 16/17, lp 3

2. Main concepts to be covered
Objektorienterade applikationer d2, förel. 4
Main concepts to be covered
Local version control
Centralized version control
Distributed version control
Systems for version control
Version control principles and concepts
Version control with GIT
Distributed workflow
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3
DAT055, 16/17, lp 3

3. Objektorienterade applikationer d2, förel. 4
Why version control?
Manual file handling does not scale well for large projects.
None or weak support for cooperation or distributed work.
A simple linear development thread is the only realistic workflow.
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3
DAT055, 16/17, lp 3

4. Objektorienterade applikationer d2, förel. 4
Local version control
Files maintained manually in directories.
Error prone.
In the rcs system, patch sets are used to keep track of the versions of a file.
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3
DAT055, 16/17, lp 3

5. Centralized version control
Objektorienterade applikationer d2, förel. 4
Centralized version control
One single repository runs on a server.
All developers are depending on the availability of the server.
Project stops if the server crashes.
Central VCS server
Version database
Version 1
Version 2
Version 3
Computer A
file
Computer B
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3
DAT055, 16/17, lp 3

6. Distributed version control
Objektorienterade applikationer d2, förel. 4
Distributed version control
Developers work independently on own complete copies of the project files.
Lower risk for data loss due to crashes.
Efficient since most changes are performed on local copies.
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3
DAT055, 16/17, lp 3

7. Distributed version control
Objektorienterade applikationer d2, förel. 4
Distributed version control
Server computer
Version database
Version 1
Version 2
Version 3
Computer A
Version database
Version 1
Version 2
Version 3
file
Computer B
Version database
Version 1
Version 2
Version 3
file
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3
DAT055, 16/17, lp 3

8. Objektorienterade applikationer d2, förel. 4
Acronyms
VC = Version Control
VCS = Version Control System
CVCS = Centralized Version Control System
DVCS = Distributed Version Control System
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3
DAT055, 16/17, lp 3

9. Systems for version control
Objektorienterade applikationer d2, förel. 4
Systems for version control
CVS
A centralized VCS. The “old standard”.
Subversion (SVN), Perforce, Bazaar, …
git
A distributed VCS.
Inventor: Linus Torvalds
First intended for development of Linux.
Resource efficient.
Widespread!
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3
DAT055, 16/17, lp 3

10. Traditional version control
Objektorienterade applikationer d2, förel. 4
Traditional version control
file C
Version 1
file B
file A Δ1
Version 2 Δ2
Version 3
Version 4 Δ3
Version 5
Revision history
Changes
Original files
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3
DAT055, 16/17, lp 3

11. Git snapshots of a file system
Objektorienterade applikationer d2, förel. 4
Git snapshots of a file system
Revision history
file C
Version 1
file B
file A C1
Version 2 B A1 C2
Version 3
Version 4 B1 A2 C3
Version 5 B2
Unchanged files are
represented as links
to earlier versions
Snapshot of
a directory
Only changed files are stored again
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3
DAT055, 16/17, lp 3

12. Version control concepts
Objektorienterade applikationer d2, förel. 4
Version control concepts
Repository (“repo”)
A database of a project’s revision history.
Commit (Checkin)
Uploading a changed file to the repository.
Checkout
Downloading a version of a file from the repo.
A note on syntax: A B
earlier version
later version
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3
DAT055, 16/17, lp 3

13. Version control concepts
Objektorienterade applikationer d2, förel. 4
Version control concepts
Branch
A parallel line of development in a project.
Merge
Creating a common line from two branches.
Conflicts may occur!
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3
DAT055, 16/17, lp 3

14. Objektorienterade applikationer d2, förel. 4
Git concepts
Working
directory
Working directory
A folder containing files
Snapshot (revision)
Staging area
Intermediate storage of files in a snapshot.
Repository
A database of snapshots of a project history.
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3
DAT055, 16/17, lp 3

15. Checkout, Stage and Commit
Objektorienterade applikationer d2, förel. 4
Checkout, Stage and Commit
Checkout
Repository
History
Working
directory
Stage
Commit
Staged Snapshot
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3
DAT055, 16/17, lp 3

16. Objektorienterade applikationer d2, förel. 4
Stage and Unstage
Unstage
Working
directory
Stage
Staged Snapshot
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3
DAT055, 16/17, lp 3

17. Workflow with local development branches
Objektorienterade applikationer d2, förel. 4
Workflow with local development branches
Repo
Working
directory
Stage
Commit
Staged Snapshot
History
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3
DAT055, 16/17, lp 3

18. Objektorienterade applikationer d2, förel. 4
Branching
feature A
main branch
V 1
V 2
V 3
V 4
V 5
V x
V y
topic branch
feature B
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3
DAT055, 16/17, lp 3

19. Merging two development branches
Objektorienterade applikationer d2, förel. 4
Merging two development branches
Version 6 contains both feature A and B
V 1
V 2
V 3
V 4
V 5
V 6
V x
V y
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3
DAT055, 16/17, lp 3

20. Objektorienterade applikationer d2, förel. 4
Merge conflicts
Snapshots V 5 and V y contain conflicting data
V 1
V 2
V 3
V 4
V 5
V x
V y
Conflicts have to be resolved by the developer(s)
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3
DAT055, 16/17, lp 3

21. Integrator-Manager Workflow
Objektorienterade applikationer d2, förel. 4
Integrator-Manager Workflow
The integrator pushes to a public repo.
Each developer clones the public repo into a local copy and makes changes.
Changes are pushed to an own public repo with write access.
The integrator pulls in and merges contributions from the public repos.
The integrator pushes merged changes to the “official” public repo.
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3
DAT055, 16/17, lp 3

22. Integrator-Manager Workflow
Objektorienterade applikationer d2, förel. 4
Integrator-Manager Workflow
Main repo
Public repo 1
Public repo 2
Public repo 3
2. Clone
1. Push
5. Push
3. Push
4. Pull in
contributions
Local repo
Integration manager
Developer 2: Main
Local repo 2 B
Developer 3: Feature B
Local repo 3
Local repo 1 A
Developer 1: Feature A
Main
Objektorienterade applikationer, DAT055, DAI2, 16/17, lp 3
DAT055, 16/17, lp 3