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

SE-2030Dr. Rob Hasker

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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

SE-2030Dr. Rob Hasker

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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

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13Image: http://svnbook.red-bean.com/

The Repository recognizes conflicts

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14Image: http://svnbook.red-bean.com/

Harry is prevented from writing

The Repository allows versions of the file to be compared for differences

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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

SE-2030Dr. Rob Hasker

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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

SE-2030Dr. Rob Hasker

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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