Version Control Systems

11 Key excerpts on "Version Control Systems"

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  eBook - PDF

  Computing Skills for Biologists

  A Toolbox

  • Stefano Allesina, Madlen Wilmes(Authors)
  • 2019(Publication Date)
  • Princeton University Press

    (Publisher)

  C H A P T E R 2 • • • • • • • • • • • • • Version Control 2.1 What Is Version Control? A version control system (VCS) is a tool to record and organize changes to a set of files and directories (e.g., the directory containing one of your projects). Over time, a version control system builds a database storing all the changes you perform (a repository ), making the whole history of the project available. When you start working on a new project, you tell your VCS to keep track of all the changes, additions, and deletions. At any point, you can commit the changes, effectively building a snapshot of the project in the repository. This snapshot of the project is then accessible—you can recover previously committed versions of files, including metadata such as who changed what, when, and why. Also, you can easily start tracking files for an existing project. Version control is especially important for collaborative projects: every-body can simultaneously work on the project—and even on the same file. Conflicting changes are reported, and can be managed using side-by-side comparisons. The possibility of branching allows you to experiment with changes (e.g., Shall we rewrite the introduction of this paper?), and then decide whether to merge them into the project. 2.2 Why Use Version Control? Version control is fundamental to keeping a project tidily organized and cen-tral to making scientific computing as automated, reproducible, and easy to read and share as possible. Many scientists keep backup versions of the same project over time or append a date/initials to different versions of the same file (e.g., various drafts of the same manuscript). This “manual” approach quickly becomes 56 ● Chapter 2 unmanageable, with simply too many files and versions to keep track of in a timely and organized manner. Version control allows you to access all pre-viously committed versions of the files and directories of your project.

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  Versioning Cultural Objects

  Digital Approaches

  • Roman Bleier, Winslow Sean M., Roman Bleier, Winslow Sean M.(Authors)
  • 2020(Publication Date)
  • Books on Demand

    (Publisher)

  95 will be relevant later on in this paper.

  3 Versioning in software development

  In software development, versioning is implemented by Version Control Systems (VCSs), first deployed in the 1970s.96 Complex software programs consist of millions of lines of code, which are intended to function smoothly together. Independent of programming style, software development is an iterative process: the developer writes the code, tests it, rewrites and enhances it, and then the cycle starts again with the testing phase. Version control software tracks the iterations or changes made to the files at each step of this iterative process providing access to each version of the file. Each version has a timestamp and an author. At any time, it is possible to identify who changed what and when. All changes, accidental or not, can be reverted, and old statuses of files can be recovered. In a collaborative software development setting, people have the possibility to work simultaneously on the same code file(s). In this case a VCS coordinates possible conflicts within the code. The rationale of these systems is the avoidance of data loss (Baerisch 1–9).

  Roughly grouped, there are two system architectures used for VCSs. On the one hand, there is the so-called centralized approach, which has been the standard for version control for many years. A code repository on a single server contains all the versioned files and clients receive the code from that central system. A well-known representative is Apache Subversion .97 On the other hand, there are distributed VCSs, such as Git , Mercurial , or Bazaar .98

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  eBook - ePub

  Computer Programming for Absolute Beginners

  Learn essential computer science concepts and coding techniques to kick-start your programming career

  • Joakim Wassberg(Author)
  • 2020(Publication Date)
  • Packt Publishing

    (Publisher)

  Chapter 11: Programming Tools and Methodologies

  Now, it's time for us to take a closer look at the development cycle. Producing software is more than just writing code. We must plan what will be coded, write the code, integrate the code we write with already existing code, share our code with other developers, test the code, deploy the code so that the application can be accessed by the users, add new features to the application, and fix bugs and errors that will show up in the code that has been released.

  To accomplish this, a development team will typically use different tools and methodologies for how things will be done and in what order. In this chapter, we will look at all the components that are part of the development process that is not the actual coding. In this chapter, we will cover the following topics:

  • Understanding what a version control system is and what it can be used for
  • Understanding unit tests
  • Understanding integration tests
  • Understanding the concept of a release
  • Understanding software deployment
  • Understanding code maintenance
  • Understanding software development process methodologies

  We have lots to cover, so let's start with an essential tool in software development: Version Control Systems.

  Understanding Version Control Systems

  A version control system (VCS ) is used to manage changes in documents, computer programs, or other collections of files. They are used by programmers to manage different revisions of their code.

  It is possible to restore earlier reversions if needed. This makes it safer to edit files, as we always have a way for us to restore what we had if we decide that the changes we made need to be reset.

  VCSs are also used so that developers can work together on the same project and, in a safe manner, work in the same source code files. Version Control Systems also keep track of who changed what in a document, and when the change was made.

  Files that are version controlled are stored in what is called a repository

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  Azure DevOps Server 2019 Cookbook

  Proven recipes to accelerate your DevOps journey with Azure DevOps Server 2019 (formerly TFS), 2nd Edition

  • Tarun Arora, Utkarsh Shigihalli(Authors)
  • 2019(Publication Date)
  • Packt Publishing

    (Publisher)

  OSS ):

  Let's look at both of the version-control systems to understand how they work. A 

  Centralized Version-Control System  (CVCS ) maintains a single central copy of your source code on a server repository. When working with a CVCS, the developer downloads the code from the server to a local workspace. Once changes to the code have been made locally, they are pushed to the

    centralized

   copy. Since each of the files in the local workspace is connected to the server, the server is aware that they are being modified, which can be useful if you intend to block someone else from making the changes while you are editing the files. Any functions against the repository (such as branching, merging, and shelving) also take place on the server, and require a connection to the server. 

  Foundation Version Control (TFVC ) is a centralized version-control system. When working with TFVC using Visual Studio or Eclipse, the IDE is in frequent communication with the server. Basic operations, such as getting the latest code or seeing the full list of history changes, cannot be done without an active connection to the server.

  A  Distributed Version Control System  

  (DVCS ) do

  es

    not necessarily rely on a central server to store all the versions of a project

  '

  s files. Instead, every developer 

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  eBook - ePub

  Foundations of Software Engineering

  • Ashfaque Ahmed, Bhanu Prasad(Authors)
  • 2016(Publication Date)
  • Auerbach Publications

    (Publisher)

  A software build is the most important artifact in any software development project. The process of making a software build starts when a software developer creates a new file. This file contains some programming source code. Now, this file should be integrated with the software build. To do this, the software developer checks his or her file in the software build. If more than one version of that software product is maintained during the project, then there could be many versions of such software builds. When there are many software builds available, the project manager decides which build to use for further development of the software product. Generally, when a new version of a software product starts to be used for the project, a new branch in the configuration and version control system is created. All the new versions of the project artifacts are then developed and saved in this new branch. The new software build is also saved in this new branch.

  We will learn about branching and configuration and version control concepts in the following sections of this chapter.

  Usage notes: Currently, CVS systems are categorized as centralized CVS systems and distributed CVS systems. The naming conventions used for CVS systems are somewhat confusing. In this book, we will use the term centralized CVS system for both centralized and distributed CVS systems. This is because, in software development projects, truly distributed CVS systems are not used. In essence, distributed CVS systems are an improvement over the old-type centralized CVS systems.

  12.2 Configuration Management and Version Control Concepts

  Configuration management and version control are carried out using a CVS system. A CVS system can be automated or manual. Nowadays, automated CVS systems are used on most software projects because several CVS tools are available in the market. Doing configuration and version control manually is very difficult and prone to mistakes, whereas CVS tools provide a foolproof and fast mechanism for all tasks involved in configuration and version control on any software project. Let us discuss CVS systems and related concepts.

  When a software product is built, many versions of various artifacts are generated. Hence, we end up having many versions of the artifacts including requirement specifications, design specifications, source code, and test documents. To incorporate any change request for an artifact, a copy of the work-in-progress artifact (if that artifact is not yet finished) or a copy of the finished artifact is first saved (with a different name) to create another copy of that artifact. Now, the requested change is incorporated into the newly created copy of that artifact. Thus, now we have two copies (versions) of the same artifact: one is without that change request and another is with that change incorporated. In the same way, as time passes by, too many versions of most of the artifacts are thus generated for various reasons. By the end of the project, a large number of versions for each of the artifacts and possibly several builds will be created.

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  Expert Python Programming

  Become a master in Python by learning coding best practices and advanced programming concepts in Python 3.7, 3rd Edition

  • Michał Jaworski, Tarek Ziadé(Authors)
  • 2019(Publication Date)
  • Packt Publishing

    (Publisher)

  Managing Code

  Working on a software project that involves more than one person is tough. Everything seems to slow down and get harder as you add more people to the team. This happens for many reasons. In this chapter, we will explore a few of these reasons and also try to provide some ways of working that aim to improve the collaborative development of code.

  First of all, every code base evolves over time, and it is important to track all the changes that are made, even more so when many developers work on it. That is the role of a version control system .

  It's very common that multiple people expand the same code base simultaneously and in parallel. It's definitely easier if all these people have different roles and work on different aspects. But that's rarely true. Therefore, a lack of global visibility generates a lot of confusion about what is going on, and what is being done by others. This is unavoidable, and some tools have to be used to provide continuous visibility and mitigate the problem. This is done by setting up a series of tools for continuous development processes, such as continuous integration or continuous delivery .

  In this chapter, we will cover the following topics:

  • Working with a version control system
  • Setting up continuous development processes

  Passage contains an image

  Technical requirements

  You can download the latest version of Git from https://git-scm.com for this chapter.

  Passage contains an image

  Working with a version control system

  Version Control Systems (VCSes ) provide a way to share, synchronize, and back up any kind of file, but often concentrate on text files containing source code. They are categorized into the following two families:

  • Centralized systems
  • Distributed systems

  Let's take a look at the preceding families in the following sections.

  Passage contains an image

  Centralized systems

  A centralized version control system is based on a single server that holds the files and lets people check in and check out the changes that are made to those files. The principle is quite simple—everyone can get a copy of the files on his/her system and work on them. From there, every user can commit his/her changes to the server. They will be applied and the revision number will be raised. The other users will then be able to get those changes by synchronizing their repository copy through an update

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  eBook - PDF

  Flexible, Reliable Software

  Using Patterns and Agile Development

  • Henrik B. Christensen(Author)
  • 2010(Publication Date)
  • Chapman and Hall/CRC

    (Publisher)

  5. A schema for collaboration/concurrent access to versions. Example Systems z 393 33.3 Example Systems In this section we will look at three example systems and describe them using the definition from the previous section. 33.3.1 RCS RCS (Tichy 1985) is one of the earliest SCM systems with restricted functionality geared towards versioning. The research challenge of the time of RCS was to mini-mize disk space usage for the repository and RCS implemented some novel storage schemes to minimize the size of the repository as well as increase performance of check-out. With respect to the definition RCS can be classified as: 1. The repository is simply a folder named RCS. This repository contains one ver-sion file per file in the workspace (versions of file ’a.x’ is stored in a file ’a.x,v’ in the repository). This file contains the complete version history and can repro-duce all versions of the file. 2. A workspace is simply a single folder in which developers commit and check-out files to and from the repository. 3. Commit is handled by a stand-alone tool ci (check-in) and check-out with a stand-alone tool co (check-out). Upon commit every file is assigned a dewey number version identity. 4. RCS only version control files, folders are not supported. Thus a configura-tion is restricted to all the files in a single folder. This configuration could be versioned by tagging all the file versions. 5. RCS uses the pessimistic concurrency model, ie. locking files. 33.3.2 CVS CVS (Berliner 1990) was created to solve two issues with RCS: the lack of handling hierarchical folders and the pessimistic concurrency scheme. CVS can be classified as: 1. The repository is a hierarchical folder structure identical to the structure of the workspace. The repository is rooted in a folder pointed out by the value of an environment variable CVSROOT (or CVSHOME )—or it can be specified directly.

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  eBook - ePub

  Beginning ASP.NET for Visual Studio 2015

  • William Penberthy(Author)
  • 2016(Publication Date)
  • Wrox

    (Publisher)

  Checking out is a way of notifying the server that you are going to be making changes to a file. By default, Visual Studio checks out a file whenever you make a change. This is important because these checked out files are the ones that Visual Studio tracks for check-in. You will not be able to check in files that have not been checked out. You may check out files in several different ways. The first way flags the file on the server so that other developers know that you may be making changes. The second way actually locks the file so that other developers cannot check in changes to that file. You need to be careful with locking a file because doing so may impact other developers trying to do their work.

  Working in a team requires more discipline than working alone. You have to be responsible for ensuring that your changes do not overwrite or break other changes made by other developers. You also have to ensure that you do your best to keep the application in a workable and functional state.

  Source control is a critical part of development. Even a developer working alone will find it very useful, especially the versioning part of the system because it provides more than simple backup functionality. It is also imperative that anyone working professionally as a developer understand how source control works and how to interact with the system.

  Exercises

  1. 1. What is a changeset, and why does it matter in source control?
  2. 2. What happens during a checkout?
  3. 3. What does TFS offer to enable a developer to determine who may have changed a file?

  What You Learned in This Chapter

  Branching	The duplication of an object under revision control (such as a source code file or a directory tree) so that modifications can happen in parallel in both versions
  Check in	The process of putting changed files into source control and creating a new version of the source code
  Check out	The process of notifying the source control system that a file is being worked on
  Labeling	The process of naming a version of the software. Labeling enables a complete version to be retained and accessed as needed.
  Merging	The process of synchronizing two different branches. Changes in one branch are merged into the other branch to ensure that edits are available in both branches.

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  Continuous Integration in .NET

  • Craig Berntson, Marcin Kawalerowicz(Authors)
  • 2011(Publication Date)
  • Manning

    (Publisher)

  Chapter 2. Setting up a source control system

  This chapter covers

  • Choosing the right source control system
  • Using Subversion on the server and client sides
  • Setting up a TFS 2010–based source control system

  Continuous integration (CI) isn’t possible without a source control system. As a matter of fact, it’s difficult to set up any reasonable software manufacturing process without one, regardless of whether you’re using CI. As soon as you progress beyond being a lonely developer spitting out code in a dark corner of a dorm room, you’ll have to think about setting up a proper place for your code to reside. You need a place you can send the fruits of your work and from where you can receive the work of your colleagues.

  In the dawn of time, there was a harsh division of functionality, and every developer had their own EXE or DLL to work on. Everyone worked on a separate part of the code and submitted their work to someone whose sole task was to integrate the code from various developers into one codebase. Those times are long gone. We now have automated systems that do the trick. They reside somewhere in the net (intra or inter doesn’t matter). Every developer works closely with the system. They push their work onto it and regularly pull the work of others out to a local construction site.

  Source control systems, also called version or revision control systems, are programs that let you manage changes in files. More important, source control systems hold the files containing the source code for your software. But generally, it doesn’t matter what kind of files are managed: documents or binary files are also welcome. As shown in figure 2.1

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  eBook - ePub

  Linux for Embedded and Real-time Applications

  • Doug Abbott(Author)
  • 2012(Publication Date)
  • Newnes

    (Publisher)

  Most of these follow a centralized client/server model where the repositories reside on a central server as illustrated in Figure 15.1. Developers “check out” individual project files, work on them, and subsequently check them back in. Most SCCs allow multiple developers to edit the same file at the same time. The first developer to check in changes to the central repository always succeeds. Many systems provide facilities to automatically merge subsequent changes provided they don’t conflict. Figure 15.1 Centralized Version Control. Some of the better known SCC systems include: • Concurrent Versioning System (CVS) • BitKeeper • Rational Clear Case • Mercurial • Perforce • Subversion • Visual Source Safe. Until 2002, the kernel development community didn’t use a version control system (VCS). Changes were informally passed around as patches and archive files. In 2002, the community began using BitKeeper, a proprietary distributed VCS. Subsequently, friction between the kernel developers and the BitKeeper people resulted in the former losing their free usage of the package. This prompted the Linux community to develop their own tool based on lessons learned while using BitKeeper. The resulting system features a simple design that runs incredibly fast while satisfying these goals: • Speed • Simple design • Fully distributed • Support for “non-linear” development • Potentially thousands of parallel branches • Handles large projects such as the kernel efficiently. So where did the name “git” come from? Git is British slang for a stupid or unpleasant person. As Linus explained it, “I’m an egotistical bastard, and I name all my projects after myself. First ‘Linux’, now ‘git’.” Introducing Git Git is a distributed VCS where clients don’t just check out snapshots of files, they fully mirror the central repository. This is illustrated in Figure 15.2. Each checkout is a full backup. So if the central server dies, it can be restored from any of the clients with little or no loss

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  Effective Software Maintenance and Evolution

  A Reuse-Based Approach

  • Stanislaw Jarzabek(Author)
  • 2007(Publication Date)
  • Auerbach Publications

    (Publisher)

  Each system release is defined as a configuration of specific versions of sys-tem components. Besides usual SCM capabilities such as version control, CVS also performs con-flict resolution and provides check-in and check-out facilities to assist parallel devel-opment. Here, we concentrate only on version control and management of system releases. We store component versions and their configurations that occurred in released systems in a CVS repository. Each such component (or component configu-ration) accommodates some combination of variant features. Typically, components are files. The following is a development life cycle for a new system release, S NEW : 1. Analyze requirements for S NEW . 2. Understand similarities and differences among S NEW and earlier releases. 3. Select from the CVS repository configurations of component versions “best matching” S NEW . We call this S NEW component the baseline . 4. Customize the selected component baseline to fully meet the requirements of S NEW . 5. Test and integrate customized components to obtain S NEW . 6. Validate S NEW to see if it meets its requirements. 00 n Effective Software Maintenance and Evolution We may need to iterate over the preceding life cycle, changing component selec-tion or customization, even revising some of the requirements, until we obtain an acceptable S NEW . In this study, we focus on issues related to component selection (Step 3) and customization (Step 4). These two activities greatly impact productivity of pro-grammers during evolution: The quality of selection determines the follow-up cus-tomization effort. In the following sections, typical problems developers must solve during these two steps are analyzed. Our analysis is based on the evolution scenario depicted in Figure 5.1. ViewRes-UI ViewRes-UI version 1.0 ViewRes-UI version 1.1 ViewRes-UI version 2.0 ViewRes-UI version 1.2 ViewRes-UI version 3.0 ViewRes-UI version 3.1 ViewRes-UI version 3.2 Figure .

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