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IVLE Design - Subversion Web Access
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===================================
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We will provide students with a web interface to Subversion. A major focus of
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the web interface is to shield new students from the details of actually
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managing a repository and just provide them with what looks like a normal file
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browser, which happens to backup their files.
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We are considering writing our own web file browser to Subversion.
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The original concept is this (as implemented in the IVLE / PynApple prototype):
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* Provide an interface to just the repository. All accesses are done directly
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to the repository, the interface knows nothing about workspaces.
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* Editing the files within the environment automatically commits the changes
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* Allow import / export of files.
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* Execute the Python programs in a special "run" directory which protects the
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* Presumably allow some kind of rollback to previous versions.
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This was problematic because it did not allow us to browse the directories
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outside of subversion (such as the execution directory).
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Our new design is to write a web-based _workspace_ browser. This will give
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students a more hands-on experience using a repository, but more importantly
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let them see what temporary files are being created and clean them up. This
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simplifies the system and reduces the amount of "magic" we have to perform
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A major advantage of this is that we no longer have to have a separate file
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browser from the repository browser. There is no "execution" directory - the
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student just works entirely within their own workspace. (If necessary this
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browser could be made to explore parts of the file system outside of a
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workspace, simply disabling the SVN features).
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This means the student can have their permanent files (say "flower-in.png") in
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the same directory as the temporary files (say "flower-out.png") and not need
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to worry about changing directories or any of those complications.
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In order to shield new students from the immediate reality of a "repository",
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we will present the system as a simple extension of a normal file system they
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are used to. (This section is written in a deliberately obtuse style; this is
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the "story" we will tell new students).
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The student is given a "workspace", with no mention of a repository. Inside
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the workspace they have "permanent files" and "temporary files". Permanent
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files are those which exist in both the (somewhat hidden) repository, and the
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workspace, while temporary files exist only in the workspace.
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Unlike originally proposed, editing and saving documents will *not*
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auto-commit. We hope to augment the editor with a "save" button (which saves
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to the workspace) and a "save-and-commit" button (which saves and commits the
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file automatically, possibly asking for a log message).
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The paradigm we present to students is: the system saves a permanent backup of
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your file when you hit "save-and-commit". In fact, each time you hit
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"save-and-commit" it saves a separate backup, so later you can go back to any
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older version. Files backed up permanently are the so-called "permanent files"
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while files which haven't been committed permanently are "temporary files".
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Editing a permanent file and saving it but not committing it results in an
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"out-of-date" file. This means you have made changes which aren't yet
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permanently backed up. The commit button either in the editor or the file
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browser will ensure these changes are permanently saved.
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A useful reason we have temporary files is you can muck around with them
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however you like, and if you don't like the changes, you can "roll back" or
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"clean up" by hitting the cleanup button. The cleanup button does *two* things
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- it "undoes" all the changes you made to out-of-date files, going back to
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their last permanent version, and it also deletes any temporary files.
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(Note: I think it would be a good idea to separate these. Have a "rollback"
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button which is seen as a large-scale undo button, which just reverts all
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out-of-date files; that is reverts uncommitted changes to files in the repo,
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and a "cleanup" button which deletes all temporary files; that is deletes any
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files which have not been added).
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(Another note: One thing which confuses *many* students, even 3rd and 4th
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year, is the difference between "add" and "commit". Hopefully we can simplify
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this so that the add button also commits? We need to decide if we want to
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enforce atomicity - that is, if we expect students to avoid committing one
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file at a time creating broken revisions - because things like the
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"save-and-commit" button on the editor, and "add-and-commit" in the file
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browser really discourage atomicity. I would argue for the best.)
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Note that files could also be out-of-date if the Python program somehow
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mangles them. In this case they should be reverted. Because of this, the
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environment could portray out-of-date files as somehow "damaged".
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A final note that the current "save" button in EditArea saves to the local
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disk - ie. it is really a "download" button. Will need to modify this so
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"save" just writes to the workspace, and have a separate download button
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(possibly only through the file browser interface).
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Multiple levels of expertise
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----------------------------
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We have identified at least two modes to place the interface (particularly,
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the file browser) into when considering the expertise levels of the users.
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We plan to have new students go into a "dumbed down" mode ("novice mode")
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which will hide certain features and details, in particular the subversion
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Essentially the novice mode will give students the impression that this is
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just a file system, with no revision control. There will be just a single
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"save" button in the editor which will save to the student's workspace.
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The "adept" mode by contrast will provide two save buttons - "save as draft"
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(or save as temporary) and "save and commit". These behave as described above.
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The question is, what does the novice mode "save" button do. It could either
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write to the workspace only (effectively meaning students are without revision
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control until they move into adept mode), or it could auto-commit each save.
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If it autocommits we may or may not let the students in novice mode browse
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their history (but if necessary, a lab demonstrator could go into adept mode
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to retrieve old versions).
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Autocommitting each save has advantages:
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* Students can be helped to retrieve old versions if they mess up or lose
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* We can check their history when we mark projects.
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* CPU drain from high volume of commits (see "unresolved issues" at the bottom).
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* Possibly hard to explain once they move into adept mode that "save no longer
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saves your history unless you click save+commit" - which is why I'm calling
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it "save as draft" and having NO button called simply "save".
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I have to say I am inclined to give even novice users both buttons. It isn't a
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terribly difficult concept to distinguish between "I am just mucking around
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with this file" and "I want to keep this".
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Alternatively, if we do dumb it down, perhaps instead of committing each save,
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we just save to their workspace and do automatic commits from the workspace
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every so often (timewise, or number-of-saves-wise).
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We have identified three levels of proficiency, which we will expect students
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to progress through as they go through the course.
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1. Novice user (students in their first or second week with no prior
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experience to revision control).
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2. Familiar user (students who have grasped the concept of revision control
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and are expected to use the system as normal developers use revision
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control for single-developer projects).
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3. Group user (students who are undertaking group work and need to use
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advanced multi-user features such as conflict-and-merge handling).
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#### Use case: First hello world ####
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Background: The student has used IVLE's tutorial section to write simple
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Python programs and also played around in the console, but they haven't used
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the file system yet. They presumably are proficient managing and editing normal
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files and folders as in Windows at home, school, etc.
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1. Student navigates to the "files" screen. They see an empty directory.
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2. Student clicks "new file". They are immediately taken to the editor with an
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untitled file. (We do not ask for filenames until they save, as most GUI
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3. Student types in the Python "Hello world" program, and clicks "save".
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(Tempting to print a warning about temporary files but this will probably just
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confuse them at first).
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4. A dialog box asks for the filename. They type in "hello.py". As with
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familiar GUI apps, they can always choose to "Save As" later.
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5. Student can now "run" the program from within the editor. (They could have
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done this before they saved - we should be able to handle running code
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which the student has not saved).
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6. Returning to the file browser, student sees "hello.py" with a "temporary
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file" icon next to it. At this stage this icon can be ignored but if the
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student enquires, a demonstrator explains that temporary files are SAVED
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but you can make permanent backups of files in case you mess them up by
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7. Student clicks "commit" and the temporary file icon goes away.
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Note that apart from the commit issue, this whole usage example is supposed to
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feel like what the students are used to with Windows applications such as file
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Explorer and Microsoft Word, Notepad, etc. (Sorry to use Microsoft metaphors
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but let's face it, that's what they know).
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Students will call directories "folders". Do we need to explain that they are
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the same thing? Should IVLE call them "folders"? Presumably the icons will
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make this rather obvious!
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#### Use case: Normal workflow, single-file programs ####
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Background: For the first few weeks, students will be primarily editing
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programs which are single-file Python programs, and will treat the file
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browser as just a directory hierarchy with backup facilities. Assume the
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student already has a Python file created as above, and it is a permanent file.
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1. Student opens the file browser where their file is stored. They click
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"edit" and are taken to the editor screen.
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2. Student edits the file, saving it frequently and running it. They are aware
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of the "temporary file" icon on the screen.
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3. Student is happy that the changes they made are positive. They click "save
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and commit". For novice students, this simply removes the "temporary file"
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icon, and the student can sleep knowing they have a permanent backup to
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4. Advanced students may have turned on the "ask for log messages" checkbox in
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their settings. When they click "save and commit", a dialog box appears
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which prompts for a log message. (This is a more advanced feature, after
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students realise the value of leaving themselves short notes for when they
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Note I am thinking of having a little icon space in the editor which shows
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* A "unsaved" icon if the user has made changes without saving (like how vim
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writes a "+" in the title bar).
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* A "temporary file" icon if the user has saved it without committing.
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* No icon if the user has just committed.
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If we are keeping a repository, this means students completely
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lack the ability to delete their permanent files (for the purpose of freeing
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up space). This means that if students reach their quota, they can't fix it.
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* Only put a quota on the head (do not penalise students for large files in
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repo). This could be abused.
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* Allow students to request (through an admin) that a file is permanently
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historically erased from the repository.
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### Novice mode CPU usage ###
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In novice mode there will be signficantly more commits than adept mode because
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of the commit each save policy (if we go down that road). Each commit takes up
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a little bit of disk space (permanently), but also is problematic because it
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takes awhile to commit and many students all using novice mode could overwhelm
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doc/notes/subversion.txt
