1. Chapter 4: Software Configuration Management (SCM)
Omar Meqdadi
SE 3860 Lecture 4
Department of Computer Science and Software Engineering
University of Wisconsin-Platteville

2. Topic Covered SCM Activities SCM Tools Why do we need SCM?
SCM Terminologies
SCM Roles
SCM Activities
SCM Tools

3. Definition
Software Configuration Management(SCM) - is the discipline of managing the evolution of complex software systems
The process of controlling and monitoring change to work products
Appropriate documentation of changes
Registering the approved software versions

4. Why do we need SCM? To answer the following questions:
Regarding last version
Who can provide me with an accurate copy of the last year’s version of the software package?
Can we be sure that the version installed does not include undocumented changes and changes that have not been approved?
Regarding current version
What is the correct version of the software module that I have to continue its coding?
What changes have been introduced in the current version?
Where can I find the full list of customers that use current version of our software?

5. Why do we need SCM?
Easy access to all previous revisions/versions/releases
To deal with conflicts in team software development:
Simultaneous updates – how to prevent one person from undoing the changes of another
Concurrent Development
Shared code – how to inform everyone who needs to know about a change
Versions – how to make changes to all affected

6. SCM Terminologies
Configuration Item: an item of software or work product which is subject to change and Needs to be under configuration management control all the time
Example: a unit of software code, a system document , Hardware unit
Change Request: a formal report that contains the request for modification in a configuration item

7. SCM Terminologies
Version : a specific instance of a configuration item (state of a particular configuration item at a given point of time)
Promotion: a version of a configuration item that has been available to other developers in a project
Release: a version of the system that has been available to the users
Repository: it stores the various releases of the system

8. SCM Terminologies Three Main Types of Releases Revisions
Intermediate Versions
Baseline Versions

9. Revisions Minor changes and corrections
May include several small changes in a revision
Sometimes we have several small revisions prior to a major baseline release

10. Intermediate (Minor) Version
Usually designed to address immediate problems as to correct defects , adaptive changes
May be done to serve only a part of the company’s clients , for a limited period until a new baseline is developed.
all clients may not be using the same version of software

11. Baseline Versions
Product that has been formally reviewed , tested and agreed to by responsible management
Milestone in the software system’s life cycle
Major releases
Have major changes , upgrades or enhancements
Serves as the basis for further development

12. Numbering Schemes for Baselines
Many naming scheme for baselines exist
A 3 digit scheme is quite common
Example: Linux Kernel Versions
2.6.0
Major Release
Minor Release
Small Revision
Linux kernels come in two flavors: stable or development
Stable kernels are production-level releases are released typically only to provide bug fixes or new drivers (Minor is even)
Development kernels undergo rapid change where (almost) anything goes (Minor is odd)

13. SCM Roles Configuration Manager Change Control Board Member Developer
Responsible for identifying configuration items
Defining the procedures for creating promotions and releases
Change Control Board Member
Responsible for approving or rejecting change requests
Developer
Creates promotions triggered by change requests or the normal activities of development. The developer checks in changes and resolves conflicts
Auditor
Responsible for the selection and evaluation of promotions for release and for ensuring the consistency and completeness of this release.

14. SCM Activities Configuration item identification Change Management
Controlling Changes
Promotion management
Release management

15. Configuration Item Identification
Not every item needs to be under configuration management control all the time
Two concerns:
What should be under configuration control?
When do you start to place entities under configuration control?
Selecting the correct configuration items is a skill
Maintainer should find relationships between configuration items

16. Which of these entities should be configuration items?
Problem Statement
Software Project Management Plan (SPMP)
Requirements Analysis Document (RAD)
System Design Document (SDD)
Project Agreement
Object Design Document (ODD)
Dynamic Model
Object model
Functional Model
Unit tests
Integration test strategy
Source code
API Specification
Input data and data bases
Test plan
Test data
Support software (part of the product)
Support software (not part of the product)
User manual
Administrator manual
: Yes

17. Change Management Change management is the handling of change requests
Change requests could be from
Users
Developers
Market forces

18. Change Request Form

19. Change Management Process

20. Proposed Change Approval
Factors to be considered as to whether to approve the change:
Urgency of the change (change priority)
Contribution of the change
Effect of the proposed change on project timetables, level of service
Estimated resources and cost of performing the change
Software quality assurance

21. Change Tracking Tools
A major problem in change management is tracking change status
Change tracking tools keep track the status of each change request
Status could be:
Rejected
Approved
Implemented
Automatically ensure that change requests are sent to the right people at the right time.

22. Implementing Change Identify the activities for
Assigning the change request to developers
Coordinating multiple changes and promotions
Identifying audits and reviews for the project
Verifying and testing implemented changes
Archiving completed change requests
Planning and control of releases

23. Controlling Changes Two types of controlling change:
Promotion: The internal development state of a software is changed
Release: A changed software system is made visible outside the development organization
Two types of management :
Promotion management
The creation of versions for other developers
Release management
The creation of versions for users

24. Controlling Changes User Master Developer Directory 1- Checkout
Promotion
Policy
Release
Policy
User
Master
Directory
Software Repository
Developer
2- Promotion
3- Release

25. SCM Directories Programmer’s Directory (Dynamic Library)
Library for holding newly created or modified entities by a programmer
Completely under control of one programmer
Master Directory (Controlled Library)
Manages the current baseline(s) and for controlling changes made to them
Changes must be authorized
Software Repository (Static Library)
Archive for the various baselines released for general use
Copies of these baselines may be made available to requesting organizations.

26. SCM Directories: Master Directory
Central database
What should be in this database?
Source Code
Documentation
Build Tools
Often need old versions of the tools to build old versions of the software
Ensures software is rebuilt exactly as the customer received it
Test Suites

27. Promotion Management Programmer/Developer File sharing management
Check out the latest version of a file/document
Make the changes
Update the database (check in)
File sharing management
Multiple people can work on the same source base without colliding
Approaches:
Locking : Locks individual files so only one person at a time can modify it
Merging: Allows multiple people to modify a source file and the system will automatically merge the changes

28. Promotion Management: Locking
Only one person can work on a file at once
Works fairly well if developers work on different areas of the project and don’t conflict often
Problems:
Problem 1: People forget to unlock files when they are done
Problem 2: People work around locking by editing a private copy and checking in when the file is finally unlocked - easy to goof and lose changes

29. Promotion Management: Merging
Several people can work on a file at once
Before committing changes, each user merges their copy with the latest copy in the database
This is normally done automatically by the system and usually works

30. SCM Change Policies
Change Policies guarantee that each promotion or release conforms to commonly accepted criteria
Example:
Promotion Policy: No developer is allowed to promote source code which cannot be compiled without errors and warnings
Release Policy: No baseline can be released without having been beta-tested by at least 200 external persons
Approaches:
Informal Promotion Policies
Formal Release Policies

31. Configuration Audits and Reviews
An audit : determines for each configuration item if it has the required physical and functional characteristics
A review : is a management tool for establishing a baseline
Audit/Review Plan:
The Configuration Items under review
The schedule for the review
Procedures for conducting the review
Participants by job title
Required documentation
Procedure for recording deficiencies and how to correct them
Approval criteria

32. Release Management Releases must incorporate changes because of:
New system functionality
Bug fixing
Hardware changes
Release planning is concerned with when to issue a system version as a release based on the following factors
Technical quality of the system
Competition
Marketing requirements
Customer change requests

33. Release Management Release creation involves:
Collecting all files and documentation required to create a system release
Configuration descriptions have to be written for different hardware and installation scripts have to be written
The specific release must be documented to record exactly what files were used to create it. This allows it to be re-created if necessary

34. SCM Tools Examples RCS (Revision Control System)
Solaris: man rcsintro
Promotion management : Locking
Little support for binaries
CVS (Concurrent Versions System)
Built on top of RCS (Little support for binaries)
Database can be remote
Promotion management : Merging
Fast
Integrates with emacs

35. SCM Tools Examples SourceSafe Clearcase
Microsoft’s entry, Integrates with MSDEV
Promotion management : Locking
Built-in web site creation tools (Project-based)
Clearcase
SCM on steroids
You create a view of the database with a config spec, which describes how to select files from the database (Slow)
Promotion management : Merging and locking
Distributed System : Several groups at different locations can work on the same database
Integrates with MSDEV

36. Case Study : CVS
Software repository that preserves changes to source code artifacts during maintenance of software systems
Hold a wealth of information and provide a unique view of the actual evolutionary path taken to realize a software system
Individual versions of a system
Software changes and their metadata
Maintenance changes are documented as commits
Each commit represents an undertaken change
Log file : file contains all commits within a period of time

37. Case Study : CVS Commit

38. Case Study : CVS Challenge problems: Huge number of commits
Version history does not keep a tag that would identify the purpose of each change