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Introduction to Version Control
SE-2030Dr. Rob Hasker
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Based on material at http://svnbook.red-bean.com/ and slides written by Dr. Mark L. Hornick
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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
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
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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 anything from a whole subsystem to a few methods within a particular class
SE-2030Dr. Rob Hasker
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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
SE-2030Dr. Rob Hasker
5Image: http://svnbook.red-bean.com/
Harry and Sally get their own respective Working Copies of the Master File in the Repository
This can lead to big problems…
SE-2030Dr. Rob Hasker
6Image: http://svnbook.red-bean.com/
Adds some method Modifies some other method
The problem to avoid:
SE-2030Dr. Rob HaskerImage: http://svnbook.red-bean.com/
Harry’s changes are still held locally…
Harry’s changes are lost
SE-2030Dr. Rob HaskerImage: http://svnbook.red-bean.com/
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Your SVN repository URL:
https://emerald.msoe.edu/svn/se2030-smithj
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The Lock-Modify-Unlock solution
SE-2030Dr. Rob HaskerImage: http://svnbook.red-bean.com/
Sally must wait until Harry releases the lock
Microsoft Visual SourceSafe follows this model
Lock-Modify-Unlock only allows a single user to edit the file at a time
SE-2030Dr. Rob HaskerImage: http://svnbook.red-bean.com/
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
SE-2030Dr. Rob Hasker
13Image: http://svnbook.red-bean.com/
The Repository recognizes conflicts
SE-2030Dr. Rob Hasker
14Image: http://svnbook.red-bean.com/
Harry is prevented from writing
The Repository allows versions of the file to be compared for differences
SE-2030Dr. Rob Hasker
15Image: http://svnbook.red-bean.com/
The Repository keeps both users synchronized
SE-2030Dr. Rob Hasker
16Image: http://svnbook.red-bean.com/
Copy-Modify-Merge is actually very easy to use and manage
Users can work in parallel
Most of the time, concurrent changes don’t overlap People generally don’t 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
SE-2030Dr. Rob Hasker
19Image: http://svnbook.red-bean.com/
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_Subversion_clients
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For more info, see http://tortoisesvn.net/
Homework
Install TortoiseSVN on your PC – needed for lab this week http://emerald.msoe.edu/resources/doku.php?
id=courses:se-2030:installing_tortoisesvn
Read more about Version Control http://emerald.msoe.edu/resources/doku.php?
id=courses:se-2030:version_control
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Links are also on course web page
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