An introduction to Version Control Systems

Editor's Notes

• #2 ...or Revision Control systems, Source Code Control systems, Software Configuration Management systems, or...\n\nThis talk was written by Jon, Tony and Ben even if only Jon and Tony are presenting it.\n
• #3 Everything changes. Anyone recognise this way of tracking changes? It’s the ‘Save as...’ approach. Do you find it works well?\n
• #4 Media Wiki, so the CS managed Wiki Service, so the CS Wiki, has quite sophisticated change tracking. Revisions. Comments. Diffs.\n
• #5 Quite a lot of other software has built-in history tracking. Here are some examples.\n
• #6 What do you typically get with something like this? What use is it?\n
• #7 Lets define some terms. We are drifting into ‘traditional’ VCSs here and away from application-specific VCS support.\n
• #8 The place where stuff gets stored. Typically looking like a directory tree. Might be a single local directory or on a central server. In the case of a ‘distributed’ VCS there might be lots of repositories but with support or transmitting and synchronising changes between them (the latter being deep magic).\n
• #9 The act of taking a copy of something to work on. Typically only you see your subsequent changes until you take further action.\n
• #10 In many systems you check out all (or a significant lump) of the repository. This is your private working copy, or working tree. You may need to refresh it to take account of changes made by others.\n
• #11 The act of updating the repository with your changes. Once you’ve committed a change then others can see it. \n\nCommits are normally accompanied by a comment describing the changes, what they are intended to achieve, etc. Serve at least three purposes: make it easier to find a particular change; provide documentation to remind you what you did; provide documentation to others to tell them what you did.\n
• #12 (for “difference”). It’s normally possible to ask to see the difference between different versions of something in a repository. Easy(ish) for text files - more challenging for things like images, videos (but see link)...\n\n[Many VCSs store revisions _as_ diffs (to save space), but that’s not directly relevant]\n
• #13 Some VCSs let you ‘lock’ a file while you are working on it to stop any one else also making changes. Slows development, esp. when people forget! Modern systems rely instead on merging (see next).\n
• #14 Modern systems let people work on the same file at the same time. When changes are checked in they systems try to merge them together. Providing they affect different parts of the file they can do this automatically - if not then human intervention is needed. Modern systems also need to do merging to support branching.\n
• #15 Getting a bit advanced. Sometimes you want to work on a new version of something, while keeping the old version around and working on that too. E.g. maintaining version n of a software product while at the same time developing version n+1. Branches let you do this _and_ transfer changes made in one branch to another.\n
• #16 "To a man with a hammer, everything looks like a nail."-Mark Twain. How to identify real VCS nails.\n
• #17 Had to add sccs!\n\nGiven a liking for “free” (as in speech and/or beer), the highlighted products are probably of most use.\n
• #18 Had to add sccs!\n\nGiven a liking for “free” (as in speech and/or beer), the highlighted products are probably of most use.\n
• #19 Had to add sccs!\n\nGiven a liking for “free” (as in speech and/or beer), the highlighted products are probably of most use.\n
• #20 Had to add sccs!\n\nGiven a liking for “free” (as in speech and/or beer), the highlighted products are probably of most use.\n
• #21 Had to add sccs!\n\nGiven a liking for “free” (as in speech and/or beer), the highlighted products are probably of most use.\n
• #22 Had to add sccs!\n\nGiven a liking for “free” (as in speech and/or beer), the highlighted products are probably of most use.\n
• #23 Had to add sccs!\n\nGiven a liking for “free” (as in speech and/or beer), the highlighted products are probably of most use.\n