Introduction to Version Control

1
Introduction to Version Control
Based on material at http//svnbook.red-bean.com/
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The stages of developing a software application

• Requirements Analysis
• High-level Design
• Plan
• Low-level Design
• Implementation
• Unit Test
• Integration
• System Test
• Deploy
• Maintain

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In many cases, multiple projects run concurrently

• New features are typically being added to the
  next version
• While at the same time, defects need to be
  corrected in existing releases

4
On a single project, a team of software engineers
work together toward a release

• All team members work on the same code and
  develop their respective parts
• An engineer may be responsible for an entire
  class
• Or just a few methods within a particular class

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Files have to be shared among developers on a
team project

• Shared files can be kept in some type of
  Repository where they can be accessed and worked
  on by multiple individuals

Harry and Sally get their own respective Working
Copies of the Master File in the Repository
Image http//svnbook.red-bean.com/
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This can lead to big problems
Adds some method
Modifies some other method
Image http//svnbook.red-bean.com/
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The problem to avoid
Harrys changes are still held locally
Image http//svnbook.red-bean.com/
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Harrys changes are lost


Image http//svnbook.red-bean.com/
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The Lock-Modify-Unlock solution
Microsoft Visual SourceSafe follows this model
Sally must wait until Harry releases the lock
Image http//svnbook.red-bean.com/
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Lock-Modify-Unlock only allows a single user to
edit the file at a time
Image http//svnbook.red-bean.com/
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Lock-Modify-Unlock has its own drawbacks

• Harry has to remember to release his lock before
  Sally (or anyone else) can acquire the lock in
  order to edit
• Sally has to wait for Harry to finish before
  editing
• Harry might be adding some new methods
• Sally just wants to add a few comments to an
  existing method

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The Copy-Modify-Merge Solution
Image http//svnbook.red-bean.com/
13
The Repository recognizes conflicts
Harry is prevented from writing
Image http//svnbook.red-bean.com/
14
The Repository allows versions of the file to be
compared for differences
Image http//svnbook.red-bean.com/
15
The Repository keeps both users synchronized
Image http//svnbook.red-bean.com/
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Copy-Modify-Merge is actually very easy to use
and manage

• Users can work in parallel
• Most of the time, concurrent changes dont
  overlap
• People generally dont edit exactly the same code
  simultaneously
• Amount of time spent resolving conflicts is
  nearly always less than the time that would be
  spent waiting for a lock to be released

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Is Lock-Modify-Unlock ever needed?

• When two or more people need to work on the same
  file, the simultaneous changes may not be
  mergable in all cases
• MS Word documents
• Image documents
• EA design documents

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The Repository can also manage and track
differences between parallel revisions of a
document

• Typically, a software product will undergo
  revisions (2.0, 2.1, 3.0) while the original
  version continues to be maintained

Image http//svnbook.red-bean.com/
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Subversion is an open-source version control
system that is available for many platforms

• Windows
• Mac
• Linux
• Many current open-source projects (like Eclipse)
  use Subversion to maintain source code control
• http//subversion.tigris.org/

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Subversion in SE2030

• The Subversion Repository for SE2030 is installed
  on emerald.msoe.edu a Linux server accessible
  via the MSOE network
• In order to access the Repository, you need a
  Subversion Client that can read and write files
  to and from the Repository on the server

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The TortoiseSVN Subversion Client

• TortoiseSVN is a SourceForge open-source client
  application for the Windows platform
• There are similar client applications for Mac
  and Linux
• Mac - http//scplugin.tigris.org/
• Linux (KDE) - http//kdesvn.alwins-world.de/
• Wikipedia comparison of various clients is at
  http//en.wikipedia.org/wiki/Comparison_of_Subvers
  ion_clients

For more info, see http//tortoisesvn.net/
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Homework

• Install TortoiseSVN on your PC needed for lab
  this week
• http//emerald.msoe.edu/resources/doku.php?idcour
  sesse-2030installing_tortoisesvn
• Read more about Version Control
• http//emerald.msoe.edu/resources/doku.php?idcour
  sesse-2030version_control

Links are also on course web page